Besides water, an RV gray tank (or “grey” if you trend more British) takes in lots of greasy, sticky substances. These include food particles & residue from preparing meals and washing dishes, soap, shampoo, toothpaste & even body oils. After a while, it can gum up your holding tank sensors, causing a false reading on your tank monitors.

Cleaning out the gray tank and sensors is a really simple task, since there’s a readily available liquid designed to break up all of the crud that can build up in the tank: automatic dishwasher detergent. The gel type is easy to flush down the drain, and goes right to work breaking down and dislodging greasy build-up.

To calibrate the holding tank monitors in your RV, follow the steps outlined in our video:

To clean your gray tank, simply choose a day when you’re about to take a long road trip to a full hook-up RV park. Just start with about a half-full gray tank, pour about one cup of automatic dishwashing detergent gel (NOT standard dishwashing soap like Dawn or Palmolive… you DON’T want something that’s going to suds up!) into one of the sinks, and wash it down the drain with plenty of hot water. Then spend a few hours on the road, allowing the sloshing action in the tank to work with the detergent to break up any nasty gunk that’s accumulated. The longer and twistier the road the better, but a few hours of agitation should be plenty.

Once you arrive at your full hook-up campground (a dump station will of course work fine as well), simply pull the gray valve and dump the tank. All of the greasy gunk that was stuck to the tank will get flushed out with the water.

If your “3/4” or “full” light is the one staying on, start your trip with a fuller tank, which will ensure good water agitation on that sensor. But since the heaviest buildup is generally in the lower part of the tank, 1/2 tank or so should provide a good combination of water and empty space for strong agitation and sloshing as you drive.

If the first try doesn’t clear up the problem, just try it again on your next long road trip. It’s so easy and inexpensive that another attempt is no big deal. Once your tank is clean, your sensors should work fine and any odors you may have been experiencing should be eliminated or reduced as well (yes, gray tanks can smell too).


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