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Old 07-05-2021, 08:08 PM   #1
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THOR #8078
Unknown plumbing connection

I am replacing the bathroom sink faucet on my 2014 Palazzo. When I removed the access panel I found the connections I expected but also found an unexpected device. It appears to have a cold water inlet but I am not sure where the outflow tubing goes. I have a filter near the water pump so I would not expect a second filter. Any ideas? Picture attached is upside down
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Old 07-05-2021, 08:18 PM   #2
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I would suspect that's a backflow preventer device... is the white flex tube going to the cold side of the faucet?

former 2014 Palazzo owner : )
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Old 07-05-2021, 08:32 PM   #3
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Backflow preventer makes sense but the tubes do not go to the faucet. They both go down through the floor, toward the water pump area. If its a backflow preventer not sure why they routed it up to under the sink area. Maybe not enough room?
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Old 07-05-2021, 09:48 PM   #4
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My son found the solution by googling "Black plastic thing under RV sink. It is the backflow prevention for the black tank flush line.
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Old 07-05-2021, 09:57 PM   #5
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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.
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Old 07-05-2021, 09:59 PM   #6
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Originally Posted by rudyhehn View Post
My son found the solution by googling "Black plastic thing under RV sink. It is the backflow prevention for the black tank flush line.
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Originally Posted by javelin View Post
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.
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Old 07-05-2021, 11:55 PM   #7
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Yes. That is what it is. An anti siphon valve for the black tank flush. It has to be mounted higher than the top of the tank and generally needs to be accessible (because they fail surprisingly often - making a soggy mess when they do). One side goes to the flush inlet and the other to the sprayer in the tank.
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Old 07-07-2021, 02:01 AM   #8
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Yes. That is what it is. An anti siphon valve for the black tank flush. It has to be mounted higher than the top of the tank and generally needs to be accessible (because they fail surprisingly often - making a soggy mess when they do). One side goes to the flush inlet and the other to the sprayer in the tank.
Yep... I had one fail in a barely year-old Grand Design trailer. It was behind an access panel in the bathroom... water EVERYWHERE!! Lucky yours is easily accessible, and they're simple and cheap.

I learned my lesson to pay attention when flushing the black tank...
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Old 07-08-2021, 12:00 AM   #9
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Yep... I had one fail in a barely year-old Grand Design trailer. It was behind an access panel in the bathroom... water EVERYWHERE!! Lucky yours is easily accessible, and they're simple and cheap.



I learned my lesson to pay attention when flushing the black tank...


When mine failed I decided not to replace it. I just abandoned it. Found that I could access both lines in the basement and just connected them together with a one way Sharkbite fitting. Since itís a dedicated system and there are now two one way valves and I only use it while Iím standing right there I think the risk of back flow is actually very close to zero. I understand the code just decided not to follow it in this case.
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Old 07-08-2021, 02:11 AM   #10
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When mine failed I decided not to replace it. I just abandoned it. Found that I could access both lines in the basement and just connected them together with a one way Sharkbite fitting. Since itís a dedicated system and there are now two one way valves and I only use it while Iím standing right there I think the risk of back flow is actually very close to zero. I understand the code just decided not to follow it in this case.
Sometimes you just gotta live on the edge... just keep a sharp eye out for those vacuum break police

Seriously though, I agree - a one way check valve is an educated person's fail safe. I once put a check valve in my main sewer in a house I used to own... heavy rains would flood the sewers and cause backups in basements. These houses were built when rainwater was dumped into sanitary sewers... against code now. One time cleaning that mess up was all it took...
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Old 07-10-2021, 09:59 PM   #11
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I would say it is a vacuum breaker and not a backflow preventer.
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Old 07-11-2021, 03:52 AM   #12
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Yes, correct. Actually a vacuum break is an anti-siphon device. Mine "failed" when the spring loaded seal stuck in the halfway position... neither open or closed. That allowed water from the black tank flush to flow up and out of the vent, flooding the bathroom. At least it wasn't funk water...

I tend to agree with pete'sMH... while they're required to pass plumbing code, they can be a nuisance on a MH... especially when they bury them hidden behind a wall! If they put in high quality brass ones with higher quality seals they might be more reliable.
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Old 07-11-2021, 05:11 AM   #13
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When needed, replace it with a Watts brass vacuum breaker. You will need to get the Shark Bite 1/2 inch to PEX slip fit connections as well.

https://www.amazon.com/Watts-Technol...5976507&sr=8-9
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Old 07-11-2021, 11:09 AM   #14
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This is an old thread but to the OP it is for the black tank flush and the only reason it shows up there is because it needs to be mounted 6 inches or higher above the toilet and that was a convenient place to do that. The water input should come from the tank flush connection in the service bay. Check out the attached instructions for installing the black tank flush.
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