How to Treat Gray Water Tanks on an RV

How to Treat Gray Water Tanks on an RV
Every water source except for the toilet in a recreational vehicle drains into the gray water tank. The toilet drains into the black water tank. Just because the toilet does not drain into the gray water tank does not mean that the gray water tank will not develop a bad odor. Kitchen scraps that go into the kitchen sink drain and dead skin and dirt that goes into the sink and shower drains feed odor-causing bacteria in the gray water tank. Fortunately, regular gray water tank maintenance is simple and quick to do. A good gray water tank cleaning routine is to treat the tank every time you dump the black water tank.


Difficulty: Moderate

Things You’ll Need:
  • Tank treatment product
  • Tank treatment product
Step 1
Close the gray water tank, which is accessed through an exterior compartment at the rear of the RV. Read the RV owner's manual for instructions on how to close the gray water tank if you do not know how. The gray water tank should be treated and emptied each time the black water tank needs to be emptied. When the black water tank is close to being 3/4 full, the gray water tank should be closed and treated.
Step 2
Pour 1 to 2 oz. of RV holding tank treatment through a sink drain in your RV. RV holding tank treatments are available at RV and camping supply stores. Many, but not all, of the holding tank treatments are safe to use in both the black water tank and the gray water tank. Before use, check the package directions to ensure that the treatment is safe to use in the gray water tank. A lot of campgrounds do not allow recreational vehicles to use their dump station facilities if the RV holding tanks contain formaldehyde-based tank treatments. If you are unsure of the rules at the dump station you will be using, purchase a formaldehyde-free holding tank treatment. If you always keep your gray water tank closed, pour the holding tank treatment through the sink after you empty and close the tank, using the instructions in Step 6.
Step 3
Keep the gray water tank closed while you use the sinks and shower in the RV as normal. Keep an eye on the holding tank gauge to see when the gray water tank is 3/4 full. The gauge is located inside the RV, usually in the kitchen.
Step 4
Hook up the RV sewer hose to the dump station sewer connection. The RV sewer hose connection is accessed through an external compartment at the rear of the RV. Drain the black water tank first, followed by the gray water tank. Doing it in this order clears out the toilet waste from the RV sewer lines. For best results, the black water and the gray water tanks should be at least 3/4 full before emptying. The force of gravity from the full tank empties the waste more effectively.
Step 5
Close the black water tank. The gray water tank can be left open if you are boon docked and hooked up to a sewer connection, or it can be closed. Boon docked or not, the black water tank should always be closed and allowed to fill to at least 3/4 full before emptying.
Step 6
Flush 2 to 4 oz. holding tank treatment followed by 2 gallons water into the toilet. If you are keeping your gray water tank closed, pour 1 to 2 oz. holding tank treatment into a sink followed by 1 gallon of water. If you are leaving your gray water tank open, wait to pour the holding tank treatment into a sink drain until you are ready to close the tank.

Tips & Warnings

To prevent damaging your gray and black water tanks, only put products in the holding tanks that are safe for septic tanks or RV holding tanks.

Article Written By Rose Kivi

Rose Kivi has been a writer for more than 10 years. She has a background in the nursing field, wildlife rehabilitation and habitat conservation. Kivi has authored educational textbooks, patient health care pamphlets, animal husbandry guides, outdoor survival manuals and was a contributing writer for two books in the Uncle John’s Bathroom Reader Series.

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