B&B model 571 vaccum Break

[woody6244]

Black tank flush line has a vaccum breaker that leaks lot of water inside coach. Why do I need this part it seem like unreliable part. Why should I not delete it with pipe fittings?

[Lt Dan]

It prevents contaminated water from the black tank flush from flowing backwards out the flush connection in the wet bay and allows the water in the line after the vacuum break to flow down into the tank. Replace it with a brass version which is more robust and reliable.

[FatChance]

You need it so black water in your black tank doesn't siphon out of the black tank, back down the flush line and into the RV park's fresh water supply or possibly your fresh water tank/system.

It is easy to replace. When you do, use a brass vacuum break from a place like Home Depot. They are much more reliable than the cheap plastic versions. When you install it, also install a brass backflow preventer between the vacuum break and the black tank (prevents sewer gas from reaching your vacuum break). Do it right, once.

This is what the replaced brass parts look like once installed:

[TheRod]

Fat Chance do happen to have part/order numbers on the products you installed?

[FatChance]

No, I just went into the plumbing department at Home Depot and found the appropriate 1/2" brass pipe fittings by asking the old guy who works there. Ask for a 1/2" brass vacuum break, a 1/2" brass backflow preventer, a 1/2" male by 1/2" male brass adapter and some pipe dope or Teflon tape. Show the guy the picture I posted and he will know. They are standard, readily available plumbing parts available at any plumbing supply source anywhere. Under $20 at the most and easy, just install using the existing PEX connectors (vertical is input, horizontal is output to black tank). When you install the brass backflow preventer, make sure the arrow points to the black tank (away from the vacuum break). 20 minute job, tops.

[PetesMH]

I eliminated mine after several failures and resulting messes! I just used a shark-bite one way valve between the flush line and the tank. I understand the purpose of the vacuum breaker (and the code that requires it). But the black water isn’t going to siphon backward through a valve, couldn’t get into the fresh tank anyway as there is no connection to it and isn’t a risk to the shore water system as I only flush while I’m standing there doing it. The one way valve is FAR less failure prone than the vacuum breaker anyway.

[FatChance]

The cheap plastic vacuum breaks installed in RVs also have a built-in backflow preventer. They use both for good reasons. Vacuum breaks fail (that is what this thread is about). And backflow preventers fail as well, there are many threads here about that. The two different valves do two separate functions so having both is a good idea.