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[16ACE27]

Originally Posted by rudyhehn

My son found the solution by googling "Black plastic thing under RV sink. It is the backflow prevention for the black tank flush line.

Originally Posted by javelin

I suspect it may be used for the black tank flush system. They mount the anti-backflow valve high typically to allow a water separation via gravity when you stop using the flush system. This help ensure there is a microbial separation between black tank flush injector and the flush water source. That is my "WAG" anyway. If that is what it is, there are a few folks on this forum that have had the anti back flow valve fail (sometimes it is inside the wall space) and leak water everywhere. You are lucky that it is at least easily accessible......assuming.....that is where it is connected.