Water mystery under vanity sink

[Jon Wells]

Hi all,

The area under our (water closet) vanity sink has a habit of getting wet.  It has been doing this randomly (at least it seams random) for a couple of years now. At the beginning of this when the amount of water was not as bad, I was assuming things like the sink drain joints which so commonly get loose in RV's. I have replaced the drain, the joint seals, and the faucet, yet no change.  Now when we find that it has flooded, the water is all over the place.  I cannot tell where it is coming from.  There are two things I'm wondering about under there.  One is the drain's under sink vent.  I checked it, and it seems fine.  The other item is a bit of a mystery (see attached picture).  I'm assuming it is a check valve with arrows pointing from blue to red, which I assume is cold to hot.  Does anyone know what this is for?  Can I just cap them off?

Thanks,
Jon Wells
2006 Monterey Ventura IV

[Roy Warren Co-Admin]

Jon,
When does it happen?  I had a leak but only when I flushed the black tank.  It was a check valve high under the sink.  The repair was to cap that valve.  No more problems.  I also capped the check valve to the sink and all we have ever noticed is a little slower drainage from the sink.  Good luck.
Roy Warren

[Joel Ashley]

I have the same coach, Jon.  If memory serves correctly, that is the vacuum breaker (aka check valve, back flow preventer, etc.) for the San-T-Flush, which should be below that room in your water bay.  It presumably keeps contaminant from the black tank flush operation from getting back into the fresh water source.  Such valves have to be positioned a certain distance above the device they serve.  You may need to replace the vacuum breaker. 
https://swanindustries.com/products/copy-of-pckv101-replacement-plastic-vacuum-breaker

I've seen lots of threads about this on RV forums, and here as well as I recall.  Some suggest, before replacing the device, that there may be debris fouling the diaphragm, and it might be cleared by removing the two screw atop the valve and inspecting inside.  That may entail removing the valve or maneuvering it to where such an endeavor is plausible.  That's a lot of "may"s and "might"s, but worth a shot, given the hose clamp methodology used on our era rigs could require special tools.  Private Message forthcoming.

I think our breaker is imperfect also, but I never tried a repair before we stopped traveling 8 years ago.  So let me know how you make out.

Joel

[Don and Kathy DuCharme]

Like Roy, we had a similar problem several years ago and it was the flush for the black tank.

[Gene Obie]

I also had leak under the sink during black tank flush due to this vacuum breaker. Replacing the part solved the issue.