Black tank backflow preventer leaks

[Mooresoc]

I’m a brand new Keystone owner and noticed a small leak in the bay storage. I narrowed it down to the bathroom sink where a backflow preventer keeps black tank from flushing into water source. I saw a lot of people saying these plastic ones break easily so I replaced it with a brass version. Still leaks. So, I made sure the fittings were tight with plumbing tape. Still leaks. So, I’m considering removing it all together and replacing it with a standard elbow since my source is a separate and specific black tank flush hose and shut off from possible contamination. My fear is that when I don’t have the hose hooked up, won’t it just leak all the way into the control area where the black tank flush valve is? Other thoughts?

 

[Notanlines]

Odds are at this point that you may have replaced the valve with the water flow in the wrong direction. It is very common for the factory to install these valves incorrectly. At least give this a try. Check and see if it is in the proper direction.

 

[Mooresoc]

Thanks for the response! I did check the flow as I saw similar posts about that. I followed the line from the black tank flush inlet and made sure that the arrow of the backflow preventer was entering the black tank and not the other way around.

 

[sourdough]

Is the brass valve itself leaking or the connections going into it? If it's the connections something isn't right in the way they are connected - they don't (shouldn't) lead once properly attached.

If you wanted to you can remove the anti siphon valve completely, install a couple of elbows on the two pipes with a small tubing bridge between them and eliminate the valve completely. If you do that use a vacuum break on the end of your flush hose like the one in the link.

https://www.tractorsupply.com/tsc/p...MItPi5x5rehwMVmkB_AB3qGAfiEAQYAyABEgLXNfD_BwE

 

[Jester-KEY]

Mine started leaking in my previous RV because I was using the black tank flush with the black tank gate valve closed. This builds pressure in the black tank and forces it out of those connections. Never run your flush with the gate valve...dump valve ...closed.

 

[johnnyb-FRF]

Mine sprang a giant leak when I ran water through it. I think that when I winterized the trailer last year and ran water through this to clean out the tank, some stayed in there (in the first few inches of the line from the outside). Then it probably froze. Like all backflow valves (for example the anti syphon valve on my home sprinkler system) you cant have water in it during a deep freeze. I think this probably is what happened. I guess i have to replace it. Actually, I think I may just by pass it and have the cleanout valve pipe directly into the black water tank. This was a giant hassle.

 

[DutchmenSport]

I'm a bit confused. You say your leak is in the "bay". Most black tank flush back flow preventers are located under the bathroom sink. Is the leak actually at the back flush preventer or somewhere else?

 

[NH_Bulldog]

Mine started leaking in my previous RV because I was using the black tank flush with the black tank gate valve closed. This builds pressure in the black tank and forces it out of those connections. Never run your flush with the gate valve...dump valve ...closed.

If your black tank pressurizes with the valve closed, you have bigger issues going on. You have a 1 1/2” abs pipe that vents the tank through the roof. If that is blocked and causes your tank to pressurize and leak, then you need to figure out why and get it fixed ASAP. I have been using the tank flush on multiple campers for years and years and have never had a leak OR had my tank pressurize.

Recently though, I started back-flushing the black tank with the grey tanks and that is so easy and works so well I might never use the flush again!