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Old 05-20-2022, 04:04 PM   #1
TDeakins
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Black Tank Backflow Lines

I have two white lines running up the wall behind the hot and cold water lines to my bathroom sink. Couldn’t be in a worse place. These lines are joined at the top by a black colored device of unknown purpose. One of the white lines is leaking where it is joined to this device. It doesn’t leak all the time or even often, but it’s a mess when it does. It has persisted since I bought it two years ago and I have just now determined where the leak is. At first I thought it was the water lines … it is not. Then I suspected it might be the lines to the clothes washer … again, it is not. My question is; what is this “rig”? … what purpose does the device serve? … how do I make it stop leaking? In doing research, I found some old forum threads that refer to it - or something like it - as a “black water tank backflow restricter”. Okay, so just what is that, anyway?
 
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Old 05-20-2022, 05:07 PM   #2
Carl n Susan
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That is the anti-backflow device for the black tank flush lines. They are known to be a problem. You can replace it with another one - the brass ones last longer - or cut the lines down in the basement, join them together, and bypass the valve all together. Be sure to add an anti-backflow device at the black tank flush connector in the convenience center
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Old 05-20-2022, 06:29 PM   #3
TDeakins
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Quote:
Originally Posted by Carl n Susan View Post
That is the anti-backflow device for the black tank flush lines. They are known to be a problem. You can replace it with another one - the brass ones last longer - or cut the lines down in the basement, join them together, and bypass the valve all together. Be sure to add an anti-backflow device at the black tank flush connector in the convenience center
Many of the parks I’ve stayed in have anti- backflow devices on their potable water points. Is this the same device I should install on the flush connection?
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Old 05-20-2022, 07:56 PM   #4
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I think these things are the backflow preventers Carl refers to…
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Old 05-20-2022, 11:11 PM   #5
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Mike those are backflow preventers but not the ones that Carl is talking about. The two lines that Tony is talking about are under the bathroom sink and are connected to a backflow device for the black tank rinse lines. They have a real tendency to go bad and either cause a leak under the sink or even flood the bedroom or bathroom. It is a larger black plastic one way valve that stops the water from the black tank from back flowing into the main or campground lines. If you go to the Search Engine here at the top of the page and type in Black Tank Backflow you will see plenty of posting about this and a lot of the threads have pictures of the factory installed valve. A lot of us have replaced it with a metal backflow valve from the big name hardware stores in their plumbing department.
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Old 05-21-2022, 07:10 AM   #6
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I had one of those cheap black plastic devices under the sink. Can't remember but something went wrong. I just disconnected it and took it apart - easy job back then. It is nothing but a tube with a marble in it. When water flows to the tank, the marble hits something that stops it from plugging the outlet. When reversed there is a perfect fit for the marble to stop the backflow. I just took the marble out and put it back together so I didn't have to do any refitting with the pipes.
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Old 05-21-2022, 07:55 AM   #7
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I am with Carl. Eliminate it all together. They are cheap & fail often making a very avoidable mess.
Add an external back flow valve at the convenience center port. Done
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Old 05-21-2022, 12:00 PM   #8
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Thank you all …

… since my leak appears to be where one of the white pipes connects to the black box, I’ve decided to cut the white pipes off on the storage locker and seal them up. I will use a standard back flow restricter where the hose meets the washout connection. You all are much appreciated. Thanks again
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Old 05-21-2022, 05:04 PM   #9
Tree Top Turkeys
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Mine leaked as well. I now have the black tank flush line separated in the basement with two quarter turn ball valves. To flush my tank I connect start water then open both valves.
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2018 montana 3791, back flow restricter, black tank flush, white lines

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