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RV Plumbing System Basics: Intro to RV Water Systems


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RV Plumbing System Basics: Intro to RV Water Systems

The great outdoors calls out to many an American adventurer loving to spend their vacation time “roughing it.” But with a recreational vehicle, there’s no reason to go without the home comforts of hot showers and a sanitary lavatory. Camping with an RV is the best of both worlds, experiencing nature and exploring the wilderness without sacrificing cleanliness and hygiene. 

However, if your toilet at home isn’t flushing, or your sink springs a leak, your first step is usually to call a plumber. But when you’re out in the wild, hours away from major cities, you might have to solve your RV plumbing problems on your own.

This may seem at first a little daunting, but armed with the basics of RV plumbing and how to maintain it you can feel confident you’ll know exactly what you need to do.

This easy-to-read article is here to explain RV plumbing system basics for you and make sure you’re prepared for a clean and comfortable outdoor adventure.

RV Plumbing Topics You Need to Know About:

  • RV water system basics
  • Overview of RV plumbing parts
  • How to fill your potable water tank
  • Where to empty your wastewater tank
  • How to keep the plumbing in your RV maintained

How Does Plumbing in an RV Work?

Potable Water vs. Wastewater System

The first incredibly important fact to understand is that your recreational vehicle has not just one or two—but three holding tanks. Each one has an essential and distinct purpose, and it’s critical never to mix or misuse any of these holding tanks.

This diagram for the plumbing in an RV shows the location of your tanks:


Fresh Water System

Of course, for cooking, cleaning dishes, showering, or flushing your toilets, you need to have a sizable supply of running water in your recreational vehicle.

It might surprise you that your RV fresh water tank can be as big as the RV’s gas tank. Your plumbing system can use a lot of water, so the tank will usually hold between 20–100 gallons of fresh water.

It’s not unusual for your RV to have two different fresh water inlet connections. All RVs will have a connection to fill the fresh water tank, but many RVs also have a separate inlet for a pressurized city water source connection. If you’re camping at a fully-equipped campground, they will usually provide hoses and connections for your fresh water holding tank.

Further Reading: Consider buying a water filter if you’re unsure about the water quality at your next hookup – these small devices can eliminate sediment, microorganisms & bad tastes/odor.

Because the holding tank is located underneath the vehicle cabin, the RV plumbing system also requires a pump to lift the water to your sinks and toilet and pressurize the water for your shower.

Your RV’s plumbing system probably also includes a water heater for your fresh water after the pump.

Gray Water System

Most of your interior water appliances (including your shower and sinks) will drain into the gray water tank. Gray water refers to wastewater that does not contain toilet sewage.

This RV water plumbing diagram clearly shows the separation between the two tanks and which utilities drain into each holding tank:


Although gray water is not as contaminated or dangerous as black water, it should still be disposed of safely. Both gray water and black water should typically be discharged into the municipal sewer system.

Under certain circumstances, your gray water can be discharged outdoors. But before dumping your gray water on the ground, make sure you meet all of these conditions:

  • You must be a safe distance away from surface water, such as lakes, rivers, and streams, and also from any underground drinking water source (wells or pipelines).
  • The drainage site should be thawed and porous to allow seepage. Do not discharge onto rock, pavement, or frozen ground.
  • You must have a properly sized and well-maintained grease trap in your kitchen sink. You should never discharge grease into the ground.
  • Make sure you are only using environmentally safe soaps and detergents, and never rinse hazardous materials down your sink drains.

Keep in mind that even if you follow these conditions, local land management might have other restrictions or prohibitions. Check with campground managers or park rangers first, but it’s always safest to discharge gray water into the sewer system.

Black Water System

Your toilet is the only interior fixture that drains into the black water storage tank. Your black tank (also called the septic tank) will probably be slightly larger than the gray water tank because your toilet typically cycles more water and gets more regular use than other appliances.

You might be wondering why your water system needs two separate waste water tanks. This is because the black tank requires more thorough cleaning, often requiring expensive chemicals. Diverting half of the waste water into another tank can save you a lot of money and work.

Further Reading: Consider purchasing a macerator pump to make disposal of your black waste easier.

Additionally, your black water tank should always be emptied into the sewer system. You should never purge your septic tank outdoors or even into a storm drain.

Plumbing Parts in RVs: The Components of the System

Water Pumps

You may have noticed in the earlier plumbing diagram, your RV requires a water pump to provide a fresh water supply to your sinks, shower, and toilet.

A good pump for your plumbing system will deliver from 3 to 6 gallons per minute (GPM). You won’t need the higher flow rate except when taking a shower, but you’ll certainly appreciate it then.


Your RV plumbing system will probably consist of four interior fixtures: a kitchen faucet, a bathroom faucet, a showerhead, and a toilet. If your recreational vehicle is a large luxury design, then you may also have a clothes washer.

When you’re outfitting your RV (or even the plumbing in your house), it’s always environmentally responsible to make sure your plumbing fixtures are designed to conserve water. Not only are you doing your part to help the environment, but you’re making sure that your freshwater tank can last long enough between refilling stations.

There are many options for low-flow faucets and showerheads, and you can also reduce excessive water consumption by using your pump at its slowest flow setting or using a low-flow pump. This might make your shower feel weak, but we promise you’ll still get just as clean!

Water-conservative sanitation is also an important practice when RV camping. Some helpful tips include:

  • Turn off the water during the middle of your shower (only using water for initial wetting and final rinsing)
  • Don’t run water while washing hands or brushing teeth
  • Use an alcohol-based hand sanitizer instead of frequent hand washing
  • Use disposable plates, cups, and cutlery to eliminate the need to wash dishes

Toilet Plumbing

There are a few differences between the way you use your toilet at home and how you use an RV toilet.

The toilet in your home should always have water in the bowl. However, this is not the case with RV plumbing. During off-season storage, your RV toilet should be empty of water. Also, the jostling motion of driving down highways and paved roads can cause your toilet bowl seal to discharge its water.

This is why RV toilets will have a small lever or footpad that will serve to refill the toilet bowl. For the best results, you should fill the bowl just before using the lavatory. 

Most RV toilets also include a hand-operated spray nozzle next to the seat. This can be used to clean the bowl after each use.

You can also outfit your vehicle with a low-capacity toilet. This is especially valuable for reducing your black water volume. Just be aware that this kind of water-saving toilet sometimes feels less clean than a model that uses excessive water in each flush. If your RV toilet has a spray nozzle, you might find yourself spraying so much water to clean the bowl that you aren’t actually conserving any.

Hot Water Heaters

There are three ways that you can heat cold water for your cooking, cleaning, and showering needs. Which one you choose is simply a matter of personal preference.

The first, and most typical, is with an electric hot water heater. This type of heater is convenient because your vehicle already has an electrical supply source (the battery). The downside is that each watt used for heating water is a watt that can’t be used for other appliances, and heating water requires a lot of power.

The second way is with a liquid propane (LP) hot water heater. These help heat your water quickly without using valuable vehicle battery power. Additionally, you might be able to use LP for some of your cooking appliances like your stovetop or oven. In this case, bringing a supply of LP can make your vacation more enjoyable.

LP powered heaters also have two sub-categories: tank heaters, and on-demand heaters. Tank heaters, just like electric water heaters, heat a small water tank (usually around 6 gallons). This isn’t much compared to your 60-gallon water heater at home. Also, keeping this tank hot can waste energy when you aren’t actively using hot water.

A much more efficient system is an on-demand hot water heater also known as a tankless water heater). These heaters rapidly heat the water when you need it, and don’t waste energy to heat water when it’s not in use. They also don’t require a hot water tank so save space in your recreational vehicle as well.

The third way to heat water in your RV plumbing system is through engine heat transfer. This method is energy-saving and cheap because you don’t need additional battery power or propane to heat the water. This method cools your engine while you’re driving, also. The drawback is that your engine, and your water, will cool down overnight, and you won’t have hot water in the mornings.


We have already mentioned the three water tanks involved in your plumbing system, along with their important functions. Keeping these maintained and routinely cleaned is of utmost importance to make sure your plumbing stays operational.

It’s also imperative to keep your tanks purged and empty during the winter months, or any extended periods when your recreational vehicle is not being used. They should also be well-insulated to avoid any water from freezing inside and causing damage or even ruptures.


Just like your tanks, it’s essential to keep your pipes and tubes well-insulated. Instead of copper or cast-iron pipes like in your home, RV plumbing pipes are almost always PVC, to reduce unnecessary weight on the vehicle.

Knowing where your pipes and fittings are located, or how to access them, can make a huge difference in case of a leak or malfunction. Calling a plumber to tape up a loose-fitting or tighten a valve may be expensive when your RV is parked at home, but may simply be infeasible when you’re parked at a campsite or in the wild outdoors.

Additional Useful Accessories

In addition to your plumbing fixtures, several extra accessories can be helpful to own to clean and maintain your RV plumbing system.

Potable Water Hose

The first thing you need to know about potable water hoses is that they’re almost always white. Hoses of other colors may not be rated for potable water and might introduce contaminants into your drinking water.

Take especially good care of your potable water hose, making sure that you don’t drag the ends through dirt or mud. After all, your drinking water goes through that hose.

Some potable water hoses are rated for cold weather or even have electrical heating circuits to prevent the water inside from freezing and rupturing the hose. Consider these if you plan to use your RV during the winter at fully-equipped campgrounds.

Drainage Hose

You will, of course, also need a separate hose to purge your gray and black water tanks. Luckily, the hoses and connections are different sizes, so it will be impossible to confuse them.

The discharge hose has a 3-inch diameter to make sure food particles, as well as tissue paper and sewage, can pass through it. Before using it, make sure the hose does not have any kinks or tears.

Many campsites and other locations with sewage connections may require that your drain hose be elevated off the ground. This is for the protection of both your hose and the campgrounds.

The connections on your drainage hose are not threaded, but twist-lock instead. The sewer terminal of the drainage hose usually has an elbow connector to lock into the septic system.

Water Pressure Regulator

It’s always a good idea to protect your RV plumbing from damage with a water pressure regulator. Many campgrounds and municipal water sources may provide water at pressures above 100 psi, and the recommended water pressure for your RV is only 40-60 psi.

12v Water Pump

If you’re planning to go boondocking (that is, camping without hook-ups), then you will be using only your potable water stored in the tank underneath your vehicle. Part of your RV plumbing system is the water pump, which is necessary to bring that water from the tank to your faucet.

When selecting a pump for your plumbing, they are rated on two different stats:

  • Flow rate in gallons per minute (GPM)
  • Pressure in pounds per square inch (PSI)

The pump also has a rating for amps, which is how much electrical current it draws from your battery. This is important to factor in when planning your electrical use.

Both higher GPM and higher PSI will make your sinks and showers more like the ones at home, but higher numbers will also deplete your potable water tank faster. It’s important to ration your water usage when camping in areas without water connections.

Accumulator Tank

An accumulator tank is a good thing to have to protect your plumbing system from pressure spikes. It also reduces the work that your pump has to perform when you are intermittently opening and closing the faucets.

The accumulator tank has a pressurized air bladder after the pump to provide some usable water pressure in your faucet even when the pump is off. This prevents the pump from engaging for brief moments and can extend the life of your pump.

Blackwater Expansion Tank (Portable Waste Tank)

If your black water tank is undersized and you’re planning an extended camping trip, it might be worthwhile to bring along an expansion tank or trailer. This is especially important if you’re camping in areas that have no sewer connections.

A portable waste tank provides you with some additional storage capacity if you fill up your black water tank. As mentioned earlier, it’s sometimes permissible to discharge grey water into the ground, but black water discharge is always forbidden (and simply impolite).

Some expansion tanks are made to fit inside your recreational vehicle or attach to the exterior body. Some larger expansion tanks have wheels suitable for highway use so that you can drag them behind your vehicle. 

Where to Fill Your Fresh Water Tank

What Is Boondocking (Dry Camping)?

Simply put, boondocking is camping in areas without water and sewer hookups.

City Water Supply

You will frequently need to connect your RV plumbing system to the city water supply. Sometimes you will do this to refill your potable water tank in between boondocking trips. Sometimes you will be camping at a site that has a city water connection source.

Connecting to a municipal water supply is similar to attaching a garden hose at your house. The potable water hose is nearly identical, except that it should be made of a stronger material, and also white-colored to identify it as a potable water hose.

Purging Your Waste Tanks

Every time you fill up your potable water tank, it’s a good practice to empty your wastewater tanks. This way, you’ll rarely overfill your black and grey water tanks. Be careful, though—if you regularly use your toilet more than your bathroom sink or shower, you might end up overfilling the black water tank early.

To purge your wastewater tanks, park your RV near a dumping station sewage port connection (make sure you apply the parking brake). Connect your tank to the septic system using your wastewater pipe, and open the valve on your wastewater tank. We recommend that you purge your black water tank first so you are then flushing the pipe with the relatively clean and soapy gray water.

After discharging your tanks, you should flush the drainage pipe with potable water before storing it by opening up your faucets. When your drainage pipe is discharging clear, clean water, close all of the valves before disconnecting from the septic system.

Maintenance and Repairs on your RV Water System

Maintenance and Routine Care

With some regular care and maintenance, you can keep your plumbing working well for many years without requiring any parts replacement or expensive repairs.

What to Avoid Flushing

You should never be flushing anything down your toilet other than water, waste, and tissue paper. It’s even best to use simple one-ply tissue paper to avoid clogging your plumbing system. More substantial, thicker paper towels and other obstructions can clog your drainage pipe or get stuck in your black water tank, where they can cause minor internal problems.

You should also have a grease trap for your kitchen sink. Cooking oils and grease can congeal in your gray water pipes and tank, causing blockages. Furthermore, many campgrounds will object to purging gray water into the ground if it contains substantial grease.

How to Keep the Smell Down

Your RV has an exterior air vent pipe extending from the wastewater tanks. This pipe may occasionally emit odors, but it is an unfortunate necessity. Keeping your wastewater tanks purged and routinely cleaned can cut down on this smell.

If you are experiencing bad odors inside the RV, there are a few things you can do to eliminate those odors.

First, check to make sure your sinks have a P-trap drain under the bowls. These are designed to collect a small amount of water that will block bad-smelling air from rising out of the wastewater tanks and into your vehicle.

Check to make sure your drains are not clogged. Clogs in your toilet and sinks can decay and emit odors.

Thoroughly clean your toilet and check the seals behind or underneath it. Faulty wax seals can allow odors from the black water tank to invade your RV cabin.

Finally, your bad odor problem may not be plumbing-related. Check your RV battery, as particular problems with the battery can cause bad smells that are often mistaken for sewage.

Winterization Step-By-Step

When parking your RV for the winter, follow these steps to protect your plumbing.

  1. Open the faucets, shower head, and flush the toilet to purge any remaining water.
  2. Drain all tanks, including wastewater, potable water, and your hot water tanks.
  3. Bypass the water heater by disconnecting it.
  4. Pour a gallon of antifreeze into your plumbing from the pump connection.
  5. Engage the 12-volt water pump to cycle the antifreeze through the plumbing.
  6. Flush the toilet until you see antifreeze in the bowl. Pour additional antifreeze into the drains.

Repairs and Replacements

Replacing Piping

Unless the pipes and fittings are exposed, you’ll probably want to hire a professional to replace those pipes. It can be challenging to find faulty pipes that are inside the RV walls and floor.

Replacing Your RV Toilet

Replacing your RV toilet is a manageable task. Close your intake valves and purge the water from them before beginning. Using the proper tools, disconnect the toilet from the bathroom.

Replacing the Water Heater

Just like replacing your toilet, make sure you close off the heater valves and purge the water before starting this replacement. After that, it should be a simple task to remove your faulty heater from the wall and mount the new heater.

If you’re replacing a gas heater, you also need to connect the exhaust chimney. Never operate a gas heater without a properly installed exhaust chimney, because the exhaust can fill the RV cabin quickly, causing suffocation or even poisoning.


Problems with your RV plumbing system are not only inconvenient but can be smelly or messy. Hopefully, this article has given you the confidence you need to understand and maintain your RV plumbing systems. We’ve found that even this basic information can be helpful for an RV owner with almost any plumbing problem.

If you found this article useful, please feel free to share it with other campers, friends, and family members. We welcome your comments in the comment section, especially if you have any personal experience to share with other visitors!

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