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RV Holding Tanks 101; How to Clean, Use, and Maintain RV Water Tanks

Updated: Apr 4, 2023

Plumbing on wheels is one of the best features of RV life. Learn all about your RV's holding tanks and how to use and maintain them.

Rv at a dumping station

Holding tanks are an important component of your RV's plumbing and water system; they control all the water that comes in and goes out of your RV. Whether you're new to the RV lifestyle or have some experience with RV traveling, it is important to learn how your RV holding tanks work and how to maintain them for long-term use. Read on to learn more about the different types of holding tanks in an RV.

Types of Holding Tanks in an RV

Every RV has three types of holding tanks that ensure your motorhome's water and plumbing system keeps working efficiently. These are:

  • Freshwater tanks

  • Gray water tanks

  • Black water tanks

RV holding tanks description

The size and type of these holding tanks may differ from one RV to the next. For example, larger Class A motorhomes may have larger holding tanks while smaller Class C campers may have the same gray and black water tank and a smaller freshwater tank. Before you buy or rent an RV, check whether the capacity of its holding tanks is enough to meet the needs of your family.

Let's take a closer look at the different types of RV holding tanks and their functions, applications, and maintenance requirements.

RV Fresh Water Tanks

RV freshwater tanks contain clean water that you use for drinking, cooking, washing dishes (and your hands), and taking showers. The freshwater tank is usually the largest holding tank in an RV and it needs to be filled regularly to maintain the level of water you will need as per your requirement. This holding tank is normally made of seamless polyethylene plastic and is available in a number of different sizes.

RV freshwater tank

How to Decide the Right Size of RV Fresh Water Tank

RV freshwater tanks can hold 20-100 gallons of water. But the size of the freshwater tank you will need for your RV depends on a number of factors including the size of the RV, the number of people traveling/living in the RV, and the total usage of water. Class A RVs usually have freshwater tanks that can carry 75-100 gallons of water while Class Bs and Class Cs can carry anywhere from 20-60 gallons of fresh water.

How to Fill RV Water Tank With Fresh Water

Filling up your freshwater tank is a pretty straightforward process. If you're parked at a campground or an RV park you can easily find water hook-ups. Connect your freshwater tank to the hook-up using a portable water hose and fill your tank up. You can also install a GAC (Granular Activated Carbon) filter on the line to prevent sediment buildup and clogging.

Make sure you have enough water filled up in your tank to last throughout your trip. It is always a good idea to top up your tank at RV campgrounds if you're planning to travel long-term or if you're going boondocking. When storing your RV, make sure you either empty the freshwater tank completely or fill it up to the brim to avoid contamination.

How to Clean RV Fresh Water Tank

To maintain the integrity and cleanliness of your freshwater tank, you will need to sanitize the tank periodically. To do this:

  • Use a funnel and hose to sanitize the freshwater tank

  • Drain about half of your water tank

  • Mix one cup of bleach in 4 gallons of water (for sanitizing a 40-gallon freshwater tank) and use the funnel and hose to pour the bleach mixture inside the freshwater tank

  • Add more fresh water on top till your tank is full

  • Now run the water through all the faucets and taps inside your RV for at least 2 min

  • Top off your freshwater tank with more clean water and let the water in the tank sit for 5-6 hours or overnight

  • Once the sanitation time is up, drain the entire tank through the water pump and faucets. You will smell chlorinated water

  • Fill up the tank with clean water and flush the tank again. Do this until you can no longer smell the bleach

  • Once the bleach is completely flushed out, replace the external and internal water filter

  • Fill up your fresh-water tank with clean water and you're good to go!

RV Grey Water Tank

RV grey water tank holds all the water that comes from the sink, shower, washing machine, and kitchen drainage of your RV; essentially all wastewater other than the one from the toilet. You can have one or more grey tanks for RV installed as per your need or even opt for a portable grey water tank for RV. They are also called Galley tanks and they have a lesser water-holding capacity as compared to freshwater tanks.

RV grey water holding tank

How to Decide the Right Size of RV Grey Water Tank

RV grey water holding tanks vary in size but they can usually carry up to 50 gallons of water. Since your grey water RV tanks don't have the same capacity as the freshwater tank, it is important to keep an eye on how much wastewater is filling up inside the tank. Grey water holding tank for RV holds wastewater but it isn't really septic, so most tanks can sit for a day or two without needing to be drained. But that would of course depend on how and how much water you use every day.

How to Dump RV Grey Water Tank

It is important to dump grey water tank for RV regularly. You can dump the tank at RV parks and campgrounds with designated dumping areas. Here is how to dump your RV grey tank:

  • Use a sewer hose (or the stinky slinky) and gloves when emptying your grey water tank

  • Connect one end of the hose to the grey water tank valve and the other end to the sewage valve in the dump station or RV camp

  • Open the grey water tank valve to empty the contents of the tank into the dump station

  • Once the tank is fully drained, close the valve and detach the sewer hose

  • Clean the sewer hose by flushing it with clean water and store it in a bucket in your RV for future use

RV grey water tank cleaning is also important. You can maintain your grey water tank by flushing it with detergent water periodically. Some other products like RV grey water tank cleaner, holding tank deodorants, and tissue digesters can help keep the tank unclogged and odor-free.

RV Black Water Tank

The black water tank of your RV holds all the septic waste from your RV's toilet. If your RV doesn't have a separate grey water tank, all the wastewater of your RV drains into the black water tank. This tank is one of the trickier holding tanks of your RV, and rightly so. It needs to be drained regularly and properly to maintain the integrity of your RV's water system.

Dumping RV black water tank

How to Dump RV Black Water Holding Tank

Dumping the black water holding tank of your RV may seem like a daunting task. The task can take some getting used to but practice and a few tips and tricks can make things easier. Here is how to dump your RV's black water tank:

  • Use gloves and a sewer hose to dump waste from the black water tank

  • Connect one end of the hose to the black water tank valve and the other end to the valve at the dumping station

  • Open the black water tank valve and let it empty completely

  • If you're RV comes with a built-in black water flush system, then connect a hose to that hookup (it will be near the freshwater hookup on your RV), you can also connect to a freshwater hose at the dump station

  • Close the black water tank valve and start filling it up with clean water. Do this for 2 minutes or so. You don't want the tank to overflow

  • If you don't have a black water flush system, you can also fill the tank by flushing the water in your toilet

  • Once the tank is partially full, open the valve and drain it again

  • Here is how to get rid of black water tank holding tank odor

Grey water and black water tanks are drained the same way. The external hookup for the sewage holding tank/s is the same, this means you only need to connect the hose once and you can drain both tanks. Therefore, it is recommended that you drain your black water tank first and then dump your grey water tank. The soapy water in the grey water tank can help clear and clean the sewage hose and you can remove it for RV blackwater tank flushing.


Filling RV freshwater tank

How long can water sit in an RV freshwater tank?

If you're regularly using the water in your tank, you can go almost 2 weeks without flushing your freshwater tank and refilling it. However, don't leave stagnant water in your tank for more than 2 weeks if you're not using it. It can easily become contaminated and unfit for drinking.

How much does it cost to replace an RV freshwater tank?

The cost of a new RV freshwater tank would depend on its size, build, brand, and more. Freshwater tank price normally ranges from $300-$1000.

How often do you dump RV black tanks?

You should dump your septic water tank every 2-3 days. Don't let waste sit in your black water tanks for more than 3 days or you will risk odor, buildup, and clogging of the water tank.

How do you know when your RV water tank is full?

A lot of RVs have a water-level gauge that will tell you when the fresh-water tank is full. You can also listen to the sound of the water coming from the overflow (if you're filling your tank from a city inlet) or look for a splashback (if you have gravity fill).

Can I dump my RV at home?

Normally, Yes, you can dump the grey and black water tanks into an approved residential sewer system. However, it would help if you were careful of your local ordinances and restrictions before dumping your RV at home.

Can you dump a grey water tank on the ground?

No, it is illegal to dump grey water on the ground.

Can I put RV antifreeze in my freshwater tank?

RV antifreeze is different from automotive antifreeze and is non-toxic for humans. So, in theory, Yes, you can use RV antifreeze in your freshwater tank. However, it is better to use items like a heating blanket to protect your RV's freshwater tank in freezing temperatures. If you do end up using RV antifreeze in your freshwater tank, make sure to flush it out completely before using the tank. Here is a guide to help you select the best RV antifreeze in the market.


RV water tanks are one of the best features of RV life; you get to have a fully functioning plumbing system on the road that makes sure you have enough water for all your needs. It is important to understand how your RV plumbng system and water tanks work to not only use them effectively but also maintain them for longevity. Use the guides mentioned above to make sure your holding tanks are good to go before hitting the road.

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