Black Tank Flush Issue

[Dopalgangr]

I have a 2018 Precept 31UL. Went to the local campground over the weekend and had no issues until I went to flush the black tank. (I have done this before without this happening). I emptied the black tank, then the grey like always. I then hooked up the hose to the black flush connection on the Nautilus system like always and turned on the water. I had all waste gates open. I heard the sprayers start then watched for water to go through my clear elbow. Nothing like it normally would do. Then I see all this water start streaming down from above the waste gate area then eventually running down from the tops of the storage compartment doors all the way to the front of the coach. I said HOLY SH!T and immediately shut off the water. Went inside to see a lot in the bathroom behind the toilet. I open the sink to find it all under the sink. It appears to have been coming from the device fitting in the attached picture. My question is does anyone know what that is and why it would have done this? The only thing that I can think is that I didn't use the pressure regulator on the black tank flush and it was too high and that thing is a release of some sort??

I would have thought the black tank flush was a straight shot to the black tank and its sprayers and would not have sent water into the pex under the sink. I did not have the city water hooked up and the fresh water tank was empty. I now have the dehumidifier running in the closed bathroom in hopes to dry everything out. The water was clear and it did not come from the toilet, only from that fitting. Thanks for any advice. Glen

BTW the picture needs to rotate 90 degrees clockwise for actual orientation. I still cant figure that out.

[Bmiller]

Not sure but it Looks like a vent for the sink drain, not sure why that woud happen unless your gray water tank was open and and your black tank backed up into your gray. If you didn't catch it I think you could of really had a problem. Make sure your gray valve is closed/sealed before flushing your black tank

[Dopalgangr]

Originally Posted by Bmiller

Not sure but it Looks like a vent for the sink drain, not sure why that woud happen unless your gray water tank was open and and your black tank backed up into your gray. If you didn't catch it I think you could of really had a problem. Make sure your gray valve is closed/sealed before flushing your black tank

Hmm, I always thought it was fine to have the gray valve opened during this process?

Also, hard to see from the picture but it has a Blue PEX going in at both connectors. Its not hooked to the drain at all.

[Dopalgangr]

here is a better pic with the proper orientation

[RetiredOne]

That black thing is a backflow preventer, to keep any possible water contamination from the black tank getting into the water system. Like everything else Jayco does, it's the cheapest one they can find, and often fails. You saw the result of that failure.

You can get a brass replacement one at Home Depot. They are also used on home sprinkler systems.

[Dopalgangr]

Originally Posted by RetiredOne

That black thing is a backflow preventer, to keep any possible water contamination from the black tank getting into the water system. Like everything else Jayco does, it's the cheapest one they can find, and often fails. You saw the result of that failure.

You can get a brass replacement one at Home Depot. They are also used on home sprinkler systems.

So I guess I don't understand how the system works then. Why would the black tank flush be connected to that? I would have thought that the black tank flush would be a separate system from the fresh water and faucet supplies. Shouldn't the flush be a direct connection to the sprayers in the tank and not be connected to anything else? Thanks for your thoughts.

[Dopalgangr]

RetiredOne, is this the one your talking about at Home Depot? Or is there another one that would be easier to replace the original one with? Thanks.

https://www.homedepot.com/p/Watts-3-...-3-4/203473940

OR even this one?

https://www.homedepot.com/p/SharkBit...-202721919-_-N

[Dopalgangr]

So I think I answered my own question. I traced the lines and it is a separate line that goes straight to the sprayer that I can see when I open the toilet. I guess they just put the check valve their so that it was accessible for replacement purposes. Thanks for all the help and I think I will just go with the $15 SharkBite one from HD in 1/2". I also think that since it was high pressure at the CG the pressure broke that valve and caused the leakage.

[RetiredOne]

That vacuum breaker keeps contaminated water from a full black tank from backing up into the flush line. Many people use the same water hose for both connections on their rigs.

[TCNashville]

Do yourself a big favor and get rid of that POS. You can replace it with one as mentioned above. I just eliminated mine and put a Sharkbite 90* elbow in it's place. I installed a city water inlet where the flush hose connects and it has a check valve. It's not a matter of if the vacuum breaker will leak, it's a matter of when.