Leak under bath sink

[woodman]

We own a 2013 Montana 3625RE. When I opened the driver side basement door, I noticed water dripping down from the water supply lines leading to the bathroom sink straight above the basement slam door. There are four PEX lines under the sink, a red, a blue and two whites. The water was coming from some type of water limiting switch that connected the two white lines. It was coming right out of the top of the device and not from the fittings. The red and blue were attached to the faucet and were fine. I was able to remove the device by unscrewing the compression nuts. I could not see anything that impeded it's operation, nothing was broken, but clearly it wasn't working. Fortunately, I found a local RV center that had one of these. They weren't aware of why this device was even used or why it was placed under the sink and neither do I. I installed the device, turned the water supply back on and everything is working fine. Anyone out there know the purpose of the pressure device or why it was located under the bath sink?

[CORattler]

I don't know the layout of your rig but maybe a backflow preventer?? Just a wild guess.

[rohrmann]

That wouldn't possibly be the backflow preventer that is part of the black tank flush system? I also am not familiar with your rig, but it sure sounds like that is what it is. If you could trace at least one of the lines to the fitting that is labelled as the black tank flush, that would prove it.

[WeBeFulltime]

It is in fact the back flow preventer for the black tank flush. It is common for them to fail.

[woodman]

Haven't been willing to undo the panels at this time and check to see where the tubing leads to, but I trust that you're right. It was a surprise discovery. Thanks for the input.

[Rondo]

Don't know when you got your 3625 RE but if you winterized it and did not blow out or push the "pink stuff" into the black tank backflow valve or preventer and line it could have frozen and split the valve or the line. If you were snowbirding and discovered it down there somewhere, it could just be a backflow valve that has gone bad already. This is a common happening for those valve. If you are still under warranty, I'd take it into the dealer and let them fix it! If you want to do it yourself do a search on the Search Engine above on the subject of black tank backflow valve and you'll see many a post on this problem and a couple of fixes for it also-- replace or remove. It's that simple BUT getting to it is not the easiest procedure. It's easier if it is under the sink, even though it is located up high under the sink than it is when it's located in the wall between the shower and the cabinet. Good luck and update us on what you find out!

[DQDick]

The purpose of the device is to keep stuff from your black tank from ending up in your water supply. You're going to be puzzled as to how that could happen. Some folks use their outdoor shower to provide the water for the flush, others use a Y off their incoming water line. A sudden drop in pressure can cause things to siphon back down the line and the vacuum breaker is there to stop that. How likely is it to happen, not very, but on the other hand are you willing to be the one it happens to. Most of us have replaced it with a good one or taken it out all together and use an outdoor one. Outdoor ones are fairly common since restaurants are required to have them on all hose connections. The reason it's required is because as unlikely as it is, it has happened and bunches of people got sick. Why it's under your sink? Keystone puts them wherever it's easiest to plumb based on the model they're building. Be happy you didn't get one behind the shower or behind a cabinet. Two other places they have put them.