What is this under my sink? It’s leaking

[Ohioken7]

Found this, the black valve thing connecting the white lines, leaking tonight. What is it? Hopefully the photo I attached works. If not, on my MHC 372rd we have dual sinks. On the right side, a white pex line comes up from the floor, connects to a black valve thing, then back to the white valve.

[Carl n Susan]

That is an anti-siphon valve for the black tank flush.

[Mikendebbie]

Question: I assume since I have 2 black tanks with separate flush systems - I have two anti siphon valves- correct?

[BB_TX]

Ken - Those black tank flush anti siphon vacuum breaker valves have a long history of leaking, often to the point of flooding your trailer. Many have simply removed them and connected the lines directly together, and use an external anti siphon valve. Some don't even use an external valve. The chance of dirty water being siphoned back into the public water supply is very remote in this case, but remote does not mean impossible.

Some have replaced the valve with a better quality brass valve.


MikenDebbie - I would think if you have two black tanks each having a flush connection that there would be two of those valves. One valve could not service both flush lines since each has its own connection.

[Ohioken7]

Thanks everyone for the advice.

[Theater Effects]

Sorry old thread. Does this only leak when you flush the tank or are there other times it could leak?

Obviously if it leaks replace/fix as indicated, but just wondering if it limited to only when you flush the tank.

[Daryles]

If it is defective, and you have a fairly full black tank, and you corner at speed, it is possible for the water to slosh with enough pressure to backflow.
Hence, why it is mounted high above the tank and why it is an anti-siphon, one way valve.
Cash ACME brass 1/2" FNPT anti siphon vacuum breaker valve.
https://www.lowes.com/pd/Cash-Acme-B...ker/1000385647

[BB_TX]

Originally Posted by Theater Effects

Sorry old thread. Does this only leak when you flush the tank or are there other times it could leak?

Obviously if it leaks replace/fix as indicated, but just wondering if it limited to only when you flush the tank.

That valve is only connected to the flush water line connection in the convenience center and is never pressurized unless you open the water faucet valve to it. It is not connected to any other source of water.

[beeje]

Originally Posted by Daryles

If it is defective, and you have a fairly full black tank, and you corner at speed, it is possible for the water to slosh with enough pressure to backflow.
Hence, why it is mounted high above the tank and why it is an anti-siphon, one way valve.
Cash ACME brass 1/2" FNPT anti siphon vacuum breaker valve.
https://www.lowes.com/pd/Cash-Acme-B...ker/1000385647

#1 You should not be traveling ANYWHERE with any substantial stuff in your tanks...….
#2 There is NO way for it to back flow to anything, since there is a check valve at the hose connection to the flush system.

[lundwc16]

Removed my anti siphon valve after a leak. I ran a direct line from the black tank flush & added a anti siphon valve used on lawn sprinkler systems from a big box store. I am surprised to see an anti siphon under a sink, as I was told that it should be higher than any other drain in the camper to meet "code". From the factory mine ran from the basement up behind a wall higher than the shower drain.

John

[BB_TX]

Originally Posted by lundwc16

..........
I am surprised to see an anti siphon under a sink, as I was told that it should be higher than any other drain in the camper to meet "code". From the factory mine ran from the basement up behind a wall higher than the shower drain.
John

That line is only connected to the black tank flush. Since the black tank is under the floor it only needs to be higher than that to function correctly.