It’s a question we get asked a lot: When dumping your RV’s holding tanks, can you first dump your gray tank’s contents into the black tank as a sort of rinsing process? We’ve seen a lot of longtime, experienced RVers do it, but we’re not in favor. Here’s why.

You’re outside your RV emptying your holding tanks as they’re full or you’re ready to pack up and move on. You open the black tank pull to empty the contents of that tank and move onto the gray tank(s). Some RVers then close a gate valve they may have installed between the RV waste pipe fitting and the flexible sewer hose, creating a sort of closed system. Then they open the gray tank valve, effectively moving the gray tank’s contents into the black tank as a rinsing process. The gate valve between the RV waste pipe fitting and the flexible sewer hose is opened, emptying the contents of both tanks into the RV park’s or dump station’s tanks or waste handling system.

Seems like a good idea, right? After all, you’re using the relatively clean water in the gray tank to rinse the black tank out. It’s a pretty common practice that a lot of experienced RVers do as a final process in emptying their tanks.

Well, stop it.

Although it sounds sensible, you’ve now opened a connection between your black and gray tanks. While those two tank’s contents are mixing together, what may be left behind in your gray tank could be some of the very unhealthy and potentially dangerous contents of the black tank.

Why is that a problem? Well, think about how many times you underestimated or just didn’t know the levels of your holding tanks. Have you ever been taking a shower only to have the gray tank fill up and back up into the shower while you’re in it?

By “equalizing” the black and gray tanks together, you’ve allowed any waste from the black tank to back up into the shower, sink, etc. once the gray tank reaches its capacity. Yuck!

Be a smart RVer and keep the contents of your black and gray tanks as separate as possible. If you’re looking to rinse out your black tank use the onboard tank rinser (which should be on while you empty the black tank anyway) or use a product like the Valterra Flush King Reverse Flush Valve.

Jim Tome, Owner

Jim Tome, Owner

Hi, I'm Jim Tome and, along with my wife, Debbie, the owners of Kleen Tank LLC, the national leader in RV holding tank cleaning service. We've been RVers like you since 2004 and have traveled all over the U.S. in our Airstream travel trailer. We started the business about twelve years ago and have cleaned tens of thousands holding tanks in thousands of RVs. From tiny weekend travel trailers to monstrous fifth wheels to luxurious motorhomes, I've seen just about every situation there is with RV holding tanks and waste systems. I hope you enjoy our articles; I try to post at least one per week and we've got a great library of them to cover just about every problem. Enjoy!


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