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Tech Talk => Info Articles => Tech Talk => Topic started by: Cooneytoones on February 25, 2009, 09:58 AM

Title: RV Water Systems How it works...
Post by: Cooneytoones on February 25, 2009, 09:58 AM
Sent: 11/15/2007
This is a long thread, I used multiple sources for the info and worked with as a plummer in the late 80's...figured it would be a good post since winter is upon us again. Covering the whole RV plumbing system.

Getting water into your RV:

Don't open a roof vent in the rain!  There are easier ways! The easiest is to simply connect a garden hose between the nearest potable water faucet and the city water inlet on the side of your rig. This provides you with water at pressure to all the fixtures in your rig. There are a few important points to note, however!
First of all, you will like the taste and smell of your water a lot more if you use a hose designed for drinking water, rather than just any green garden hose.
It's a good idea to have several lengths of hose, as you never know how far away that faucet will be. I have a 10 foot, a 20 foot and a 50 foot fresh water hose and use whichever one or combination of several that reach the faucet the best.
NEVER NEVER NEVER use your fresh water hose for any other purpose! Don't use it to wash the car, or (God forbid!) to flush out your holding tanks! That hose needs to be treated carefully and kept as sanitary as possible. After all, you're DRINKING this water, right?
RV plumbing was designed to operate at pressures of 40 to 60 psi and most can tolerate pressures up to about 100 psi. Unfortunately, some unregulated city water can have pressures as high as 150 psi or more. The best bet here is to always install a pressure regulator on the line coming to your city water connection. There are inexpensive pressure regulators that simply screw onto one end of your fresh water hose and they are cheap and effective insurance.

Taking your water along for the ride.  If you won't be having the convenience of a fresh water spigot at your destination, then you'll have to take water with you using your rig's fresh water holding tank. Filling the tank is as easy as hooking your fresh water hose to a nearby faucet and running water into the water tank fill opening on your rig. These fresh water fills come in many shapes and sizes.... here's a typical example:
Make sure that the tank drain valve, if there is one, is closed before starting to fill the tank. If your tank has a vent valve, it's best to open it to allow the tank to fill faster. If your tank glugs, chuffs and spits water back at you when filling, then it's likely that it has no vent or the vent is plugged or shut off somewhere. Simply slow down and let the tank fill at it's own rate. You can make the task easier by using a little fill adapter like this... it fits on the end of the hose and then slips down into the filler. A handy little device to have.

Getting water to the fixtures:
If you are hooked up to a fresh water faucet, then there ain't much to it! Hook up the hose to your city water inlet, turn on the faucet and open a faucet inside the rig to allow any air to escape. It's a good idea to purge all the sink and tub fixtures and to make sure that the water heater is filled.
If you are in a boondock or dry camping situation, you must rely on the 12V water pump in your rig to supply water under pressure to the fixtures. To get started, open a cold water faucet in the rig and turn on the pump. Having a faucet open will help the pump prime quickly. When the water is flowing nicely, close the faucet. Briefly open each faucet throughout the rig to purge out any air. Once this is done, the pump should stop running after you close the last faucet and shouldn't run again until you open a faucet somewhere. The pump is designed to pump the system up to about 40-50 psi and then a pressure sensing switch mounted on the pump shuts the pump off until the pressure drops. You are all set... just remember that your supply of fresh water is limited and conserve it! When the tank runs out, you will hear the pump speed up and the flow of water from the fixtures will slow or stop. It's best to turn the pump off at this point until you refill the fresh water tank. These pumps can run dry for an extended time without damage, but it's a waste of power to just let it continue to run, so be sure to turn the pump off when the tank runs dry.

Where does it go from here:
In a non-mobile house, once the water disappears down the drain, we can forget about it. Not so in a RV.... Every drop winds up in the holding tanks and then we must at some point deal with it again. Let's look at that block diagram again.... the waste waters from the sinks and shower are transported to the Gray Water tank through a series of pipes. Each drain has a standard plumbing trap that keeps the sewer odors from coming back up through the drain. The gray water builds up in the tank until we dump it. Similarly, the toilet dumps directly to the black water tank through a foot or lever operated valve. This valve seals off the tank when the toilet is not being flushed and keeps the odors in the tank where they belong.
In most cases, the black and gray tanks are sized slightly smaller than the fresh water tank... usually somewhere between 20 and 50 gallons each, although truly large rigs may have tanks approaching 100 gallons each. The best source of capacities information for your particular rig is either the owner's manual or the dealer. It's handy to know the actual capacities of your plumbing system because water weighs! It's safe to figure about 8 lb. per Gallon for water and waste liquids and you can see how it can add up in a hurry! A 50 gallon fresh water tank, when filled, is going to add 400 lb. to the weight of your rig. Traveling with full holding tanks can add a lot of weight and easily put your rig over it's safe operating weight. Be aware of your rig's dry weight by weighing it fully loaded, but without fresh water or propane onboard and with empty holding tanks. Compare this weight to the unit's GVWR.
GVWR - (dry weight) = available capacity for water and propane
Propane weighs about 5 lb. per Gallon.... Be careful not to overload your rig and always be aware that water has weight and must be considered as part of your payload!
Man have discovered that when dry camping or boondocking, the gray water tank tends to fill up pretty quick while the black water tank rarely ever fills up. This makes sense, as the only source of fluids for the black tank is the very efficient RV toilet. The gray water tank has to contain the liquids from all the sinks and the shower. Strangely enough, however, most RVs have black and gray tanks that are the same size! Given the above, it seems like a lot of tank capacity is going to waste here and I decided to do something about it. I designed and installed a simple transfer pump that will move gray water from the gray water tank to the black water tank. Details on the transfer pump are included below in the Enhancements section.
Occasionally, a RV manufacturer will ignore good design engineering and plumb the bathroom sink and/or even the shower into the black water tank, just because it's easier and cheaper. Beware this setup! It makes it possible to overflow your black water tank by running water in a sink or shower that common sense says is connected to the gray water tank. If your black water tank seems to fill up awfully fast, you might just be the lucky owner of one of these mis-plumbed rigs. If you suspect non-standard plumbing in your rig, the best way to check is to be at a full hookup site. Dump both tanks. Close the black tank dump valve and leave the gray tank dump valve open. Run water into all sinks and shower for several minutes and monitor the black water tank level. If water shows up in the black tank, then you have one or more sink drains plumbed to it. This doesn't mean that you must immediately sell your RV and buy another... it just means that you are now aware of a potentially annoying and destructive "feature" and you should keep a close eye on the level in your black tank. In most correctly plumbed rigs, when you completely fill up the gray water tank, the drain water will begin to back up into the bathtub or shower, which is usually the lowest point in the gray water system. This is pretty harmless.... after all, it's just soapy water and it's not going to hurt anything. However, if a sink or shower is plumbed into the black tank and it becomes completely full, then what backs up isn't going to be soapy water! Plus, it may not back up into such an innocuous place as the tub. Thankfully, this kind of problem seems to be pretty rare, so your rig is most likely correctly plumbed. Mine is not The shower and the tub both drain into the black water tank, so I have to be careful.....Thanks Winnebago.....LOL
Most folks agree that the gray water tank can be dumped anytime, no matter how full or empty, and when you are hooked up to a sewer connection, the gray water dump valve can be left open at all times. This allows the water from your sinks and shower to flow directly out of the rig and into the campground sewer system. Hey, that's easy! However, it is not a good idea to treat your black tank the same way. Black water contains a lot of ... well... call them 'solids'. RV toilets flush with very little fresh water, so these 'solids' are quite concentrated. If you were to leave the black water dump valve open while hooked to a  sewer connection, these solids tend to build up in your tank and then dry into a disgusting form of concrete. Over time, a black tank can become partially or completely blocked, leading to a highly nasty cleaning job or complete tank replacement. To avoid this, always keep the black water tank dump valve shut. Let the black water build up until the tank is at least 1/4 full and then dump it, rinsing with lots of fresh water. Waiting to dump the tank keeps all those 'solids' in suspension and the quick rush of fluid out of the tank when it is dumped helps carry most of the solids out. Whenever it's convenient, try to dump the black tank after traveling... the motion of the rig on the road will mix up the contents nicely and help break down the 'solids'. When parked for an extended period, I usually dump the black tank every couple of weeks if the weather is cool and more often when it's hot. (helps keep the odors down!) The day before I plan to dump the black tank, I shut the gray tank dump valve. This allows some gray water to build up in the tank... then, when I dump the black tank, I follow it with the gray tank to flush out the hose and help carry the whole mess down the sewer pipe to wherever it ultimately ends up.
Don't put this stuff down your drains!

Grease or oil. It will congeal in the tanks and pipes and require dynamite to remove!
Caustic cleaners or solvents. Tanks are ABS plastic and solvents can destroy them!
Flammable liquids. Duh!!!
Toxic wastes. More Duh!!!
Food scraps. Even small scraps can build up in your tanks... consider a drain screen! Click here for an example.
Don't flush anything down the toilet unless you've eaten it first!! No tampax, paper towel, bottle caps, toys, Q-tips, cotton balls, etc, etc, or you'll be SORRY!
Don't use that quilted 3 ply toilet tissue you love.... Sorry! It's best to use either an inexpensive one or two ply tissue you can get at your local food store or stick to RV toilet paper. Both work about the same, but the RV stuff is about 4X the cost! Whatever you use, it needs to dissolve fully in your tank. If in doubt, always do the jar test: take a sheet or 2 of your TP, put it in a jar 1/2 full of water and give it a shake. Safe TP will dissolve readily, bad stuff won't and shouldn't be used in your RV!
Toilet chemicals containing formaldehyde or any other crap that ends in "dehyde". Don't use this stuff! It plays havoc with sewage treatment plants and septic systems alike. Don't believe the B.S. about it being biodegradable.... it's doom and is one of the reasons that so many public dump stations have been closing.
Pine oil. Favorite ingredient of home-brew tank treatments, it will do long term damage to the seals on the tank gate valves, leading to expensive and disgusting repairs down the road.

Nowadays there are a number of enzyme and bacterial tank treatments on the market. These products are designed to stimulate aerobic bacterial action and break down the waste and kill the odors... kind of like having a miniature sewage treatment plant onboard. They carry an added benefit in being completely biodegradable and highly beneficial to RV park septic tanks and sewer treatment plants as well
If you decide to stick with old fashioned toilet chemicals, please use them sparingly and avoid using any product with Formaldehyde as the active ingredient. Most home brew toilet treatments should be viewed with a skeptical eye. Don't even consider using a home-brew remedy that has pine oil or Pine Sol in it. Pine oils will harden the seals on the dump valves and eventually cause leaks
Monitor panels

All RVs come equipped with some sort of monitor system that is supposed to tell you how much 'whatever' is in your tanks. These systems haven't changed significantly in the last 30 years and most still rely on physical conductive probes inside the tanks. Here is a simplified diagram to show you how this is all supposed to work.
For the most part, this system works pretty good for the fresh water tank and the gray water tank, but leaves something to be desired for the black tank. Most folks find that after a year or two, the sensors in the black water tank stop working. This is due to the probes getting coated with yuck in the tank and this yuck interferes with the accuracy of the monitor. There are literally dozens of expensive tank cleaning concoctions on the shelves of your local RV store and there are almost as many home-brew cleaning ideas out there... some work better than others, but nothing will fix the problem permanently. My favorite home-brew tip is to put a few gallons of clean water and a small amount of dish soap in your freshly dumped black water tank and then add a large bag of ice cubes. Drive the rig for a few hours, then dump when you arrive at your destination. The idea is that the ice cubes will scrub the insides of the tank and then melt. It's worth a try if your monitor panel isn't working right...
When it comes to the standard monitor systems installed in most RVs, they are just likely to be inaccurate in use. You can either put up with it, do a regular cleaning of the tank probes and hope that it helps, or invest in a replacement tank monitoring system. There are a couple of different ones out there on the market and they work without any probes inside the tank. One popular system uses capacitance and simply requires a couple of sensors be placed on the outside of the tank body 
Dealing with dumping:

Probably one of the least enjoyable tasks associated with RVing is getting rid of the waste water that accumulates. It's really not so unpleasant, if you do it right.
First of all, buy good quality hoses and fittings.... the heavy duty sewer hoses cost a little more but will last a lot longer and are more resistant to springing leaks. It's a good idea to have both a 10 foot and a 20 foot sewer hose. Equip each hose with the correct fitting to attach it to your rig's dump connection. It is also a good idea to have at least one set of sewer adapters to connect your sewer hose to the sewer fitting in a RV park. I use the red E-Z couplers and really like them, as they simply screw into the sewer hose, needing no additional clamps. They provide a neat leak proof connection to the park's sewer system and are quite inexpensive.
There are a number of other brands on the market as well... just pick out whichever one you like. The unused pieces can be stored in large Ziploc bags in a compartment. The flanges are removable and the elbows are designed to stay on the hose and fit either into your bumper stowage or in a custom sewer hose storage.
At the dump station or sewer connection, park the rig close enough for your dump hose to reach. Connect the hose to the rig first, then place the other end into the sewer opening in the ground. If it doesn't want to stay put, you can place a small rock or brick against it to hold it in place. A piece of wood or a leveling block can also be used. We don't want that end of the hose to jump out when we start to dump, now do we.... As a last resort, you can ask your spouse to hold onto it, but this is probably the least desirable solution, especially if anything goes wrong!
Pull the Black Water tank dump valve first. This way, you will dump the black water through the hose first, then follow it with the gray water to flush out the hose. Once the black water tank is empty, you should rinse out the tank with clean water. This can be done by dragging a garden hose into the bathroom and running water down the toilet, or you can use a special flushing stick through the toilet dump valve. Another possibility is to step on the small pedal to fill the toilet bowel full and then quickly flush the toilet. Do this a few times and it will rinse out the black tank to a small extent... If all this sounds like a hassle, (and it is!)
Once the black tank is empty and flushed out, close the black water dump valve. Now, open the gray water dump valve. As the gray water runs through the hose, you can shake it around a bit to help rinse out the inside of the hose, but be careful not to shake too hard and dislodge the hose from either the rig or the dump. Once the gray tank is empty, shut the valve and wait a few moments before disconnecting the hose from the rig. Disconnect the rig side first and lift the hose up so that any residual water drains into the dump fitting. Now's the time to rinse out the sewer hose if you like, using a water hose. DO NOT use your Fresh water hose to do this!!! Most dump stations have a water faucet nearby and sometimes even a hose, but it's a good idea to have a short section of hose of your own and only use that hose for rinsing when dumping.
Put all the caps back on. Cap off the dump connection on your rig and replace whatever cover or plug that belongs with the park sewer connection or dump station connection. Shake out your sewer hose and stow it and it's adapters. Make sure that you rinse away any spilled waste or mess, especially at a public dump station and stow your rinsing hose and close all compartments. OK, you're ready to go! ... Now, that wasn't so bad, was it? Oh... It's a great idea to wash your hands at this point.... Some folks like to use disposable plastic gloves... they put them on before starting and then just discard them afterwards. I keep a small bottle of liquid soap right in the same compartment where the hoses and stuff are stowed... makes it real quick and easy!

Most older RV fresh water systems are plumbed using gray polybutylene tubing. Most connections are made using barbed connectors made of either gray plastic-like materials or brass and either aluminum or copper crimp rings. This plumbing will resemble the picture below. There have been a lot of claims that polybutylene plumbing breaks down and eventually leaks, usually at the connections. I spent some time researching these claims and I'm sad to say that there appears to be a pretty good case against the gray stuff. One thing is certain: they aren't making it anymore! It has been universally replaced by cross-linked polyethylene tubing in most newer RVs. Identified by it's white or red color, PEX is assumed to be safe and reliable. The connections are made either with Qest fittings or the familiar crimp rings as seen below. The tool is the most expensive part.

Well, now that I've ruined your day, where do we go from here?
If all that sounds like too much work, then you are in luck! There are a number of different repair fittings available for the poly tubing that work on the compression principle. One of the brand names is QEST and these fittings are also available at most RV parts shops and hardware stores, and through most RV parts catalogs. To use these fittings, simply cut the tubing, assemble the fitting according to the package directions and tighten the compression nuts. These fittings are substantially more expensive than the more simple barb and ring ones, but are very convenient and easy to use.

Most faucets used in modern RVs are similar to those used in standard housing and many share the same parts. You can find washers and repair parts for most RV faucets and fixtures if you simply take the defective part with you to the local plumbing shop. The low pressure lines used to supply water from your fresh water tank to the water pump are common vinyl tubing, available at most hardware stores. The waste plumbing is standard household black ABS fittings with very few exceptions. Sink drains, traps, connectors and drain pipes are all standard sizes and types. Replacement parts are available at most hardware stores and the piping is usually joined using ABS plastic pipe cement and standard fittings. The only departure from standard plumbing parts are RV specific items like dump gate valves and sewer hose connector fittings and some of the external drain valves and fittings. The bottom line is that RV plumbing is easy to repair and modify. If you have basic plumbing skills, you should have no problems with your RV plumbing. For those of you without basic plumbing skills,  The most important thing to remember is to protect your RV plumbing from freezing temperatures, and we'll discuss that in the Winterizing section below.
Built in regulator:

To eliminate the problem by installing a Shur Flo regulated city water inlet. This is a great little device and is easy to add to your rig. It regulates the incoming water pressure to a safe 45-50 psi and since it's attached to the rig, it's harder to leave behind. An added benefit; this regulator seems to flow more water than the little brass ones that you attach to the water spigot. For those of you who would rather have an external regulator, they also make one set up with hose connectors. If you are unhappy with the low flow rates you are getting through your current regulator, this would be a good replacement for you. Available from most RV parts stores through the Shur Flo catalog.
Water heater bypass a must:

If you are in the habit of winterizing your RV with RV antifreeze, this little addition will save you gallons of the pink stuff! Some RVs have these installed from the factory, but for those of you who don't have one, several different brands are available. What this does is allow you to completely bypass the water heater so that when you fill your water system with RV safe antifreeze, you don't have to fill the whole water heater as well. The picture shown is a factory installed setup.... but it gives you an idea of how it works. To bypass the water heater, drain it and then close the valves on the heater inlet and outlet and open the bypass valve. Check your RV catalog.... most units are simple to install and don't require cutting any existing plumbing and simply screw onto the existing water heater nipples. One note... if you don't use antifreeze to winterize your rig, then there really isn't any reason to install a bypass....

Pressure gauge:

This is a mighty handy little item! It's a simple pressure gauge installed inside the rig to monitor water pressure in your fresh water system. It's very simple to do... just purchase a standard gauge that will read from 0 to 100 psi or more and add a tee anywhere in the freshwater plumbing. you are in the habit of not using a regulator, this gauge is a real necessity.

Expansion tank or Pressure Tank?

An expansion tank helps smooth the water flow in your RV and also allows for the expansion of  water in your water heater. If your water heater relief valve leaks or your faucets drip when your water heater is operating, then this is one for you! An added benefit is that it reduces pump cycling when operating on internal water. It's a cheap and easy installation   


Possibly the most important thing you can do to ensure the long life of your RV plumbing is to properly winterize your rig. For those of you who live in climates where it never drops below freezing, my congratulations! You can skip this section! Many of us, however, will be storing a rig in freezing temperatures during the winter months. It is critical that you take the proper precautions to protect your plumbing from freezing, or you will be faced with some nasty surprises come springtime.
To prepare your rig for winter storage:
Drain all tanks. Flush out the black water and gray water tanks and be sure to get them as empty as possible.
Drain water heater.
Drain fresh water system using low point drains if provided. Open all faucets and step on the toilet pedal as well. Get as much water out of the system as possible.
Now, you have a choice... you can either protect your fresh water piping by using a non-toxic RV approved antifreeze or you can use air pressure to blow out the remaining water in your water lines. Both methods have advantages and disadvantages. Using RV antifreeze is probably the surest method to absolutely guarantee that no pipes will freeze. Properly used, it will protect your rig well down into sub-zero temperatures. It does require a lot of flushing in the spring to get the taste out and also makes it desirable to install a water heater bypass to reduce the quantity of antifreeze used. Plus, the stuff ain't cheap.

NEVER use any antifreeze or substance in your fresh water system unless that product is specifically labeled as non-toxic and safe for use in drinking water systems. Use only antifreeze designed specifically for RV water systems!
In order to easily pump the antifreeze throughout your water system, you can install a neat little valve that allows your pump to draw antifreeze directly from the bottle. It's available from most any RV parts source.
Alternately, you can remove the existing hose from the inlet side of your water pump and attach a short piece of hose to reach into the antifreeze bottle.  Bypass the water heater if you can. If you have an ADC filter under the sink, install the manufacturer's antifreeze diverter. If you have a cartridge type filter, remove the filter element and replace the cartridge holder. Run the pump and open each fixture, allowing it to flow until you see pure antifreeze. Monitor the level in the antifreeze bottle and make sure it doesn't run dry. Remember to flush the toilet and operate the toilet sprayer if installed. Don't forget the shower head. Depending on the size and complexity of your plumbing system, you will probably need 1-3 gallons of antifreeze. If you don't have a water heater bypass, better add 6 or 10 gallons to that, depending on the size of your water heater! Once you have done each and every fixture in the rig, you should have full protection against freezing pipes in your freshwater system.
Instead of using antifreeze, you can use air pressure from a compressor to blow the water out of your fresh water lines. This method is cheaper than the antifreeze method and you won't have to flush the antifreeze taste out of your water system come spring. On the down side, however, it is extremely hard to get every last bit of water out of the lines and if sufficient water collects in a low point or valve, then it may be damaged by freezing. Plus, there are portions of the water system that blowing the lines won't clear and you must drain them manually. Still, many people prefer to use air to clear the lines, rather than deal with the antifreeze. To start with, you will need a little plug that will fit into your city water inlet and provide a fitting to connect the air compressor to. It looks like this:

Hook up your air source and set it for a max. of 60 psi. Once pressure is applied, go through the rig, starting with fixtures closest to the inlet and open them briefly, allowing the air pressure to blow the water out. Remember to flush the toilet and operate the toilet sprayer if installed. Don't forget the shower head. Once you have done each and every fixture in the rig, you should have most of the water out of your freshwater system. Remove the air source. Now, it will be necessary to remove the outlet line and inlet line from your fresh water pump and drain them manually, as the check valve in the pump prevents the air from clearing these lines. Remove any cartridge from any under sink filter and make sure the fixture is drained. Your freshwater system should now be in good shape for the winter storage months.
Now, you need to pay attention to the other plumbing systems in the rig:
Pour a small amount of RV antifreeze down each drain to protect the trap. Additional antifreeze can be poured down a sink to help keep any residual water in the gray tank from freezing.
Pour a small amount of antifreeze into the black tank through the open toilet flush valve.
Close the toilet flush valve and pour a dab into the toilet.
If you installed a gray water transfer pump or any other optional plumbing system, be sure that they are fully drained or protected with RV antifreeze.
There are a lot more steps to winterizing your rig....this just covered the ones relating to plumbing. Best source of additional winterizing info is your RV owner's manual or RV dealer.
When the summer season gets ready to start, make sure that anything you disconnected is reconnected and that all hoses and water lines are visually intact and in good condition. Close any open drain valves. If you used antifreeze, flush it out according to the antifreeze manufacturer's instructions. Now is a good time to sanitize your fresh water tank and system. Replace water filter cartridges with new ones. Refill the water heater. Apply pressure to the fresh water system and thoroughly inspect all plumbing connections and fixtures for leaks. If you did everything right at the start of the storage season, then your rig should be ready to go!
Title: Re: RV Water Systems How it works...
Post by: Froggy1936 on February 25, 2009, 04:09 PM
One thing you did not mention by name (to not put in the toilet) is kleenex This stuff will last forever in water and it makes a very good stop leak even in a 3 in pipe and in case of a spill you cannot pick it all up its very bad in the waste system and so very easy to dispose of in the toilet like you do at home Speaking from experience  Frank
Title: Re: RV Water Systems How it works...
Post by: ClydesdaleKevin on February 27, 2009, 08:50 PM
As a fulltimer I agree with almost everything here, but have to add my own 2!

First, to elaborate on a point I agree on, use a one-ply paper.  We use Scott 1000 sheets per roll.  Its soft enough unless you really need to read braille with your buttocks, it breaks down quick, and its cheap!

Second, I do NOT agree with the formaldyhyde thing.  Formaldyhyde IS biodegradable, degrades VERY rapidly, occurs naturally in anything in nature that was once a living thing and is now "rotting" away back to the basic elements, and is fairly non-toxic to the most of the bacteria that break down waste.

Formaldyhyde is a naturally occuring substance that immediately breaks down in sunlight, and will break down underground in a septic system in very little time. 

It also works SO much better to break down solids and deoderize than the so-called "natural" alternatives which aren't any more natural than gasoline.