How do I figure out what is draining into each of my holding tanks?

A very good question! While most of the answers might seem pretty intuitive — your toilet drains into your black tank and your shower goes into the gray — there are some interesting counter-intuitive situations that may be present in your particular RV. For instance, a lot of RV’s have sinks in bathrooms draining into a nearby black tank.

There’s an easy process to figure out what is going where:

1. Make sure that you have a clear piece of plastic sewer pipe somewhere between your RV’s sewer waste pipe (where tank waste exits and goes into the flexible sewer hose) and the actual sewer hose. As gross as this sounds, you want to see what is coming out of your tanks (always a good practice to monitor your tank’s health).
2. Empty all of your tanks using the gray/black/gray method. Make sure that they are completely empty.
3. Close all of the tank valve pulls.
4. With either the help of an assistant or by yourself, go inside of your RV and turn on or run water down one sink/shower/toilet/washer drain. Let them run or drain for a few minutes (you want some build-up of water in the tank that the sink/shower/toilet/washer drains into). Turn off the water after a few minutes.
5. Go outside and pull each handle until you find which one is tied to that fixture. Write it down on a note and close the handle when the water is done emptying.
6. Repeat until you’ve run and tested every water fixture.