Leak under sink while emptying tanks

[BryanA]

Keystone Laredo 5th wheel.

I have found that while flushing the holding tank, and if someone runs the toilet, something under the kitchen sink sends water everywhere.

What's happening???

[jsmith948]

There is a plastic vacuum breaker attached to the pex lines that feed the tank flush. The location of this valve varies from one model trailer to another. On our Cougar, it is hidden up under the bathroom vanity. if the fittings have worked loose or if the plastic housing is cracked it will leak when using the tank flush. If you do a forum search, you will find that many of us have simply removed the breaker - replacing it with a couple of elbows - and then adding a hose bib anti-siphon at the tank flush inlet.