Vacuum break under vanity

[xxiiiliv]

I finally looked into the break, because I couldn’t get the black tank flush to work. Looked at the break and noticed it was installed upside down, as per the instructions on the cap. Is this a common occurrence, or, does it not matter. From what I saw of it, when installed correctly, the valve is in the down position (which looks like it vents under the sink), and when water is applied, the valve goes up, blocking the vent and sending water to the tank. Is this correct?

 

[Qwazert]

I'm not a plumber, but I believe these things are installed to prevent "liquid" from getting drawn back into the hose.
The tank flushing manifold is actually underwater at some time during the flush, so I think it is part of the plumbing code that a vac-breaker needs to be used to prevent the black water from being drawn back into the potable supply.
Mine started to leak two seasons ago, so I removed it completely and use one fitted to the hose instead.

 

[xxiiiliv]

Understood. My question is, does the orientation of the valve matter

 

[Qwazert]

Depending on the construction of the item, they may be orientation-specific.
Most of the vacuum breakers I've seen are vertically mounted, and there is definitely an UP and DOWN side to them. Many of them use a small plastic float.

 

[SaltyVetAdventures]

I'm confused. The vacuum breaker under the vanity? You mean the mushroom looking thing under your bathroom sink? That's for the gray tank and not the black tank. It shouldn't have anything to do with your black tank flush.

Black tank flush should have a one way check valve installed inline to only allow water into the black tank and nothing to come back out.

Please correct me if I am wrong or misunderstanding. I know your ask about the orientation but you bring up two different things?

 

[xxiiiliv]

Ok…

 

[xxiiiliv]

Oh, and this answered my question about orientation as well

 

[SaltyVetAdventures]

Ok…View attachment 11283

That is what I was talking about when I mentioned a one way check valve. I think of a vacuum break like what's behind the shower or behind the toilet. Learn something new everyday! This is under the vanity in your RV?

 

[xxiiiliv]

Yep, and like you, I never gave it a moments thought. I can see it being upside down could be problematic

 

[xxiiiliv]

It’s connected to the flush inlet and apparently the valve is pushed upward by water pressure when flushing the tank out. Something occurred to me as well. I think it takes a good amount of water pressure to make it work, so, I’m probably at fault for it not working