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What is an RV Gray Water Tank? (Definition, Types, Purposes,…)

Written by Philip Lopez / Fact checked by Paul Lemaire

what is an rv gray water tank

I’m often confused about how to tell several water tanks apart from each other. I know that a fresh water tank is for clean water, while a black one is for toilet waste. But what is an RV gray water tank?

A gray water tank is a container for all the waste from your sinks and bathroom shower. It has a capacity of 30-70 gallons and like all other tanks, it needs to be drained regularly.

If you want to know more about gray water tanks, continue reading.

Table of Contents

Gray Water Tank Definition

Grey water storage tanks hold all the liquid runoff from drains other than the toilet. This includes the wastewater from indoor showers and sinks. Let’s say you’re washing the dishes or taking a bath, the dirty water goes into the gray tank for later dumping.

It’s called gray water for a reason. When the soapy water mixes with food remnants and other waste materials inside the camper grey water tank, the color of the liquid turns murky or gray.

In some RV models, the bathroom sinks drain to the black water tank because some axles are too small to fit grey water holding tanks. It’s not a problem if you have a large black water container. What you should avoid is a shower draining into the black tank because the latter will fill up faster.

Sometimes, you may see gray tanks set up for house as well; people use them to store waste for treatment and reuse.

Types of Holding Tanks


Don’t confuse gray water tanks with other types of holding tanks in your RV. They serve different purposes.

  • Fresh water tank: This tank stores potable water for your RV. It supplies water for washing dishes, cooking, and showering for camper.
  • Grey water tank: The water used in cooking, showering, and dishwashing goes to the grey water tank.
  • Black water tank: This tank holds the black water coming from your toilet, including urine, toilet paper, and fecal matter. Black and grey water in RV are different. While grey water can be reused for toilet flushing, black water is totally unsafe.

Size And Capacity

The size of the gray water tanks corresponds to the RV size, but the average is 30-70 gallons. A larger RV means a larger gray water tank to accommodate the number of people living in it.

  • The largest RVs, which are commonly Class A motorhomes, can have a gray tank as big as 70 gallons.
  • Class C motorhomes are mid-range RVs with a gray tank capacity ranging from 50 gallon to 60 gallons, though 35 gallons exist as well.
  • Class B motorhomes, which are the smallest, have a maximum capacity of 30 gallons for their gray water tanks.
  • A travel trailer grey water tank would have about 46 gallons maximum.
  • Meanwhile, fifth wheels can have the largest containers, up to 95 gallons with a lower limit of 50.

Material Construction


Most gray water tanks are made of polyethylene resin to ensure resistance and durability from harsh elements. Unlike steel, these plastic tanks won’t corrode when exposed to water over time. They’re also lightweight, making them easy to install in any location.

When cleaned and maintained properly, polyethylene can last for more than ten years. Look for a UV stabilizer addition if you want to install the tank on an elevated area where the sun is always up. For an undermount grey water tank, look for extreme durability and corrosion-resistant strappings.

Purposes of an Rv Gray Water Tank

A gray water tank isn’t made for solely collecting wastewater from all your sinks. This tank also serves as a means to recycle and reuse wastewater for other RV purposes. All you need is a good recycling system kit to filter the grey water from your laundry and shower.

The filtered grey water can be used to flush the toilet or irrigate the plants around your camper. By doing so, you save fresh water for drinking. Some filtering systems even allow the recycling of grey water into drinking water.

Watch how to convert grey water to potable water in this video. Recycling dirty water in an RV to make it drinkable

How Does It Work?

In the RV grey water tank plumbing system for a stationary RV, grey water exits into one drain line. All the wastewater stays in the tank until it’s full and ready to be emptied.

It’s easy to determine when the gray water tank is full because it usually comes with an indicator. If it doesn’t, you can watch how the water moves in the drains. Your grey water tank is probably full if the water doesn’t drain in the kitchen sink when washing the dishes.

To empty gray water tank, hook the ends of the drain hose to your tank’s outflow valve and the dumping station drain. Open the valve and let the wastewater drain. Once done, close the valve, then remove and clean the drain hose.

If you want to camp longer without the worries of dumping, you can get some extra grey water portable tanks. These small tanks have a capacity of about five gallons.

Frequently Asked Questions


How long does it take for a gray tank to fill up?

It all depends on your gray tank’s capacity and how often you use water. A 32-gallon tank may fill up within three days under normal use. If you use the water sparingly, you produce less waste and hence, should empty the gray tank after a week or so.

What happens when the RV gray tank is full?

You’ll easily know when the grey water tank is full because the wastewater goes back up and drains slowly. It’s especially a headache if you’re washing the dishes. The soapy water will fill the kitchen sink, and no amount of plumbing can flush the water into the pipes.

When this happens, empty the gray tank immediately.

Can you pour RV gray water on the ground?

Not all states and cities allow the dumping of gray water on the ground because some soap ingredients can contaminate the water sources of the area. If you must make the dump, make sure that the local area allows it. Research is key.

How to keep your RV gray water tank clean?

After each dump, run all your taps to flush the gray water tank of food waste and other debris. Add your favorite RV gray water tank cleaner to kill the bacteria and odor. If you can’t get a special cleaner, make your own RV grey tank treatment with a dishwashing liquid or vinegar.

Let the cleaning solution work its magic inside the tank for about 30 minutes or even a day. Once done, empty the tank and rinse with fresh water.


I hope you know what is an RV gray water tank at this point. It’s one of the three containers that make your RV life easier. Make sure that you choose the right tank capacity so that you can camp longer in any remote location.

Tell us your experiences with RV gray tanks in the comment section below. If you like this article, please share it with your friends.

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