RV Gray Water Tanks Meaning

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What are RV Gray Water Tanks?

Gray water is the term for water that has flowed down the drain of your sink or shower.

In an RV, that water has to go somewhere, and where it goes is into the gray water tank.

And when something goes in, it must come out. This means that gray water tanks must be emptied periodically. You can dump your RV’s waste tank at a sani-dump station or into your campsite’s sewer hookup (if equipped).

The size of your RV’s gray water tank depends on several factors such as what kind of RV you have, and the size of your RV. So it is important to know the size of your RV’s tank and keep track of how many days of “typical” use you can get out of your RV before you have to empty the gray water tank.

Most RV’s also have a sensor to signal when the tank needs to be emptied.

Note that “gray water” is a different from “black water. Blackwater is a term for the waste that flushes down the toilet. (So waste materials and liquid from flushing the toilet.)


Key Takeaways 

  1. Gray water is waste water that emptied down the drain of a sink or shower
  2. In an RV, gray water collects in a gray water holding tank
  3. Your RV’s gray water tank must be emptied into a sani dump station or into a campsite’s sewer hookup



RV Gray Water tank meaning
RV Gray Water Tank Meaning



Understanding RV Gray Water Tanks

Having gray water tanks (and black water tanks) in your RV provides the convenience of being self-contained.

At least until the tanks are full, at which point you’ll have to hookup to a dump station or campsite sewer connection to empty the tanks using your RV sewer hose.

RV’ers will generally empty their black water tanks first, and then the gray water tanks. When they empty their blackwater tanks – which consists of heavier toilet waste – there may still be some yucky sewage in the sewer hose.

Emptying the gray water second means the waste water from the sinks and showers will flow down the sewer hose and help flush fecal matter and other materials along the sewer hose and into the dump station.


If you are staying at a campsite that has a sewer hookup, do not keep the waste valves on your gray water or black water tanks always open. You may think that keeping the valves open will prevent a stinky accumulation of waste in the tanks, but the opposite can actually occur.

If the dump release valves are kept open on the waste tanks then water may flow out of the tanks, but not flush waste materials with it.

In a gray water tank this means that soap scum, dirt and oil from the dishes or your body will stick to the walls of the tank. This build-up can lead to nasty smells…the opposite of what you want.

So even if you’re hooked up to a sewer connection at a campsite, keep the waste release valves closed and then dump the tanks periodically.





Related Terms

RV Black water tank

A tank in an RV that holds the waste flushed down the toilet


Full Hookup Campsite

A campsite that has fresh water, electricity and a sewer hookup.



Partial Hookup Campsite meaning

A campsite that has fresh water and electrical hookups, but not sewer. (This means you’ll have to head to a sani dump station to empty your gray water tank and black water tank.)




RV Shore Power

When you hook up your RV to an external supply of AC electricity.




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