Black tank flush line vacuum breaker

[ColoradoPriorMarines]

it took a bit, but found the Montana vacuum breaker in the wall between kitchen cabinet and shower. Cut hole in cabinet wall and removed plastic vacuum breaker.

Replaced with a brass swing-check valve - does anyone think that would be a problem?

[BB_TX]

Had to google "brass swing check valve" as I had never heard that term. But it is described as "Brass Swing Check Valve to stop water from backing into a municipal water supply" so I see no reason it shouldn't work.

[mtlakejim]

"swing check" is what we call them in the oilfield but it should be noted we don't always use the same terms as the plumbing industry. The other style is called a "ball check" and has a spring loaded ball. The swing check will only work if it is in a horizontal position. If you need to set it up in a vertical position then you have to go with the "ball check". In another thread I have a picture where I used a swing check as a secondary protection from back surge inside the water supply cabinet (outside). Chances of the black water flush actually flowing backwards and contaminating the fresh water lines is very slim but since I was hard piping the flush line to a fresh water supply line I wanted to make absolutely sure. I used the "swing check" in a horizontal position and because it was a lot cheaper and I happened to have one on hand. I would have felt slightly better using a "spring check" as they perform better though.... How was the plastic valve situated? Did it have a spring and ball in it or a flapper?

[ColoradoPriorMarines]

a swing check is what i used - in horizontal position. The vacuum breaker was horizontal , it is a cheap plastic piece similar to one on a sprinkler system but a lot cheaper.

i dont see much of chance the tank would back up that high either.

[mtlakejim]

Is this actually a vent line for the tank so it won't pressurize or is it a vac breaker so the black water won't back up thru the black water flush line?

[BuilderBob]

It's a one way valve for the water it's not a vent for the black tank it stops the water from flowing backwards when you shout of the water flow to the black tank.

Bob & Carol
Washington St
2017 352RL 2008 Dodge 3500 DRW crew cab 4x4 LB 6.7L

[mtlakejim]

Based on Builder Bob's comment, I would speculate that if you install a check valve on the flush line where you make the connection in the water connection compartment then you should not need the other line at all. But I suspect that the black water tank needs some sort of vent to relive pressure when you turn on the flush line or they would burst? Besides there needs to be some way for H2S gas to escape?

[Butch & Kathy]

On my unit the vacuum break was under the bathroom sink. When it started leaking I cut it out, threw it away and bypassed with a piece of tubing. I installed a new water inlet with built in check valve. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[fatcatzzz]

Originally Posted by Butchy

On my unit the vacuum break was under the bathroom sink. When it started leaking I cut it out, threw it away and bypassed with a piece of tubing. I installed a new water inlet with built in check valve. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

X2 ^^^^
Replaced mine with a 1/2"street ell and a close nipple. Use a check valve on the black tank flush inlet. NO chance of a leak inside.

[DQDick]

I removed ours and use an external one that you can get at most hardware stores.

[Rookey]

X3 on the external. Works great and now my bathroom cabinet does not get wet.

[mtlakejim]

Post some pics of the location of that valve. I haven't looked yet but it would be good to know where to look when I do!