RVers always think the worst of their holding tanks is the black one. We’re here to tell you that gray tanks can be just as bad – or even worse!

Gray (or grey) water tanks collect water from drains in the galley or kitchen, the shower (or bathtub, if you’re lucky enough to have one) and, sometimes, the sink(s) in the bathroom(s). What you’ll find in the gray tank is soap, food particles, and parts of “us” including hair, skin, and other bodily waste (other than urine and feces that goes down the toilet, of course). But most gray tanks contain mostly water.

Should you leave your gray tank valves open?

Now, some RVers like to leave their gray tank valves open all the time, most of time until a day or two before they’re ready to dump the black tank, or when they are doing laundry (if they have a clothes washer). In all but the last case (laundry), we don’t recommend that you keep your gray tank valve open.

Why? When a tank valve is open, water, or at least, the more liquid contents of the tank, tends to seep out slowly, leaving solids behind. This tends to be more of an issue in black tanks where the “solids” are larger, but in gray tanks it can be a problem too.

As water or liquid seeps out, any remaining solids (food particles, coagulated soap, hair and skin, etc.) can start to rot and create clumps. Also, because your tank is hot and wet, mold can start growing. That can cause terrible odors and even affect those with sensitive respiratory systems.

Yuck! What’s that stuff?

What you’ll start to see coming out of your gray tanks are chunks of this decomposing material and growing mold. Unfortunately, both are very sticky and can stay inside of your gray tank, causing problems like odors and even clogs.

Leave those tank release valves – black and gray – closed until you are ready to empty your tanks. Then follow the best practices guide in emptying your tanks to keep them healthy, working properly, and with minimal problems.