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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 to many American adventurers who love spending our vacations “roughing it.” But with an RV, there’s no reason to go without hot showers and sanitary toilets. Camping with an RV is a great way to experience nature and explore the wilderness without sacrificing cleanliness and health. 

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

This might seem like a challenge, but it can be simple to learn and understand the basics of RV plumbing with a little help.

This easy-to-read article will 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.
  • Keep your RV plumbing maintained.

How Does RV Plumbing Work?

Potable Water vs. Wastewater System

The first important fact to understand is that your RV has not just one or two—but three holding tanks. Each one has an essential and distinct purpose, and it’s critical not ever to mix or misuse any of these holding tanks.

This RV plumbing diagram shows the location of your tanks:


Fresh Water System

Of course, if you want to cook, clean dishes, shower, or flush your toilets, you need to have a sizeable supply of running water in your RV.

It might surprise you that your RV fresh water tank can be as big as its 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 pressurized city water. 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 RV 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 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 the gray water is not as contaminated or dangerous as the 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). Environmental Health Services recommends a distance of at least 30 meters.
  • The drainage site should be thawed and porous to allow seepage. Do not discharge into 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 rinsing hazardous materials down your sink drains.

Keep in mind that even if you follow these conditions, the 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 the other appliances.

You might be wondering why your RV water system needs two separate wastewater tanks. RV plumbing systems divert wastewater into two different tanks because the black tank requires a more thorough cleaning, which often requires expensive chemicals. Diverting half of the wastewater into another tank can save you a lot of money and work.

Further Reading: Consider purchasing a macerator pump to make the disposing 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.

RV Plumbing Parts: The Components of the System

RV Water Pumps

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

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

RV Plumbing Fittings

Your RV plumbing system probably consists of four interior fixtures: a kitchen faucet, a bathroom faucet, a showerhead, and a toilet. If your RV 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 fresh water storage 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 the water while washing hands or brushing teeth.
  • Use an alcohol-based hand sanitizer instead of frequent hand washing.
  • Use disposable plates, cups, and cutlery instead of washing dishes.

RV 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 toilet 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 U.S. highways and off of paved roads can cause your toilet bowl seal to discharge its water.

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

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

You can also outfit your RV 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 conserving any.

Hot Water Heaters

There are three ways that your RV can heat water for your cooking, cleaning, and showering needs.

The first way, and most typical, is with an electric hot water heater. This type of heater is convenient because your RV has an electrical supply source (the battery). The downside is that each watt used for heating water is a watt that you can’t use 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 your valuable 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 water 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 is not very 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 tankless water heaters). These heaters rapidly heat the water when you need it, without wasting energy to heat the water when it’s not in use. There’s no need for a hot water tank taking up space in your RV, either.

The third way to heat your 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 RV plumbing system and their important functions. Keeping these tanks maintained and routinely cleaning them is of utmost importance to make sure your RV plumbing stays operational.

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


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 big 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 might be simply infeasible when you’re parked at a campsite or in the wild outdoors.

Additional Useful Accessories

In addition to your RV plumbing fixtures, it’s helpful to own several extra accessories 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 hoses 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 toilet 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 source 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 RV. 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 RV 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 RV 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 RV or attach to the exterior RV body. Some larger expansion tanks have wheels suitable for highway use so that you can drag them behind your RV. 

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 city water supply connections.

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 sink or shower, you might end up overfilling the black water tank early.

To purge your wastewater tanks, park your RV near a 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 that you can flush the pipe with the relatively clean and soapy grey 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 RV plumbing working well for many years without requiring any RV parts replacement or expensive repairs.

What to Avoid Flushing

You should never flush anything down your toilet other than water, waste, and toilet paper. It’s even best to use simple one-ply toilet paper to avoid clogging your RV 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 cleaning them 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 into your RV.

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 under the toilet. 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, because 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 RV plumbing.

  1. Drain all tanks, including wastewater, potable water, and your hot water tanks.
  2. Open the faucets, shower head, and flush the toilet to purge any remaining water.
  3. Bypass the water heater by disconnecting it.
  4. Pour a gallon of antifreeze into your RV plumbing from the pump connection.
  5. Engage the 12-volt water pump to cycle the antifreeze through the RV 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 your toilet before beginning. Using the proper tools, disconnect the toilet from the RV 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 campers 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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