What happens when I overfill my RV’s holding tanks?

Well, if you are lucky, any overfill in your black or gray tank will travel up your vent pipe and make a mess on the roof. However, the answer is a bit tricky and depends on the exact plumbing setup of your RV. Some RVs have back-check valves built into the plumbing system, preventing waste from backing up into the shower or tub, toilet bowl, or sink. This is normally a feature of higher-end RVs, so most of us aren’t that lucky.

For most RVs, gray tank overfill will back up to the lowest point, which is usually the shower. How many of us have taken a shower only to look down and see the water rising? Yep, you waited too long to dump that gray tank! In the black tank, there’s a higher probability that waste will travel up the vent pipe, but we have also seen it back up into the toilet (talk about a mess!).

In the worst case, waste can burst your tank(s), making a mess everywhere and very expensive repair. It’s always best to monitor your tank sensors (or whatever method you use) and dump those tanks on a regular basis.