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Old 06-20-2022, 07:59 AM   #1
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Leak under sink when do black tank flush

Recently a mysterious red pipe under the bathroom sink has started leaking. The pipe comes up from the floor, does a u-turn and goes back down to the floor. There is a brass valve at the u-turn. My husband and I thought we had it fixed with some tightening, but then, we we did a black tank flush, there was water all over the floor again. We found a discussion of a similar problem on the internet, relating to a Forest River. They called the part a black tank flush anti-siphon check valve and said it was easy to replace.

Anyone had a similar problem with their Monaco and is the diagnosis right?

Can we get the part on Amazon?

Our pipes have these little metal clamps that look like they're impossible to take off. Do we need to mess with them when replacing the valve?

Thanks!
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Old 06-20-2022, 08:22 AM   #2
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Quote:
Originally Posted by VickyfromNZ View Post
Recently a mysterious red pipe under the bathroom sink has started leaking. The pipe comes up from the floor, does a u-turn and goes back down to the floor. There is a brass valve at the u-turn. My husband and I thought we had it fixed with some tightening, but then, we we did a black tank flush, there was water all over the floor again. We found a discussion of a similar problem on the internet, relating to a Forest River. They called the part a black tank flush anti-siphon check valve and said it was easy to replace.

Anyone had a similar problem with their Monaco and is the diagnosis right?

Can we get the part on Amazon?

Our pipes have these little metal clamps that look like they're impossible to take off. Do we need to mess with them when replacing the valve?

Thanks!
My black tank check valve started leaking, except mine was behind the aquahot blower on the outside wall and I couldn't hardly reach it. I cut the pipes and tied them together. Then I bought a check valve that I screw into the black tank flush in the water bay then screw the hose into that.

I've never had an rv where that back flow preventer didn't fail and I always bypass them that way.

You need to buy pex tools, pex fittings, and pex clamps. Clamp remover tool, clamping tool, and pex cutter. Buy those and keep them in your rv. They don't cost much.
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Old 06-20-2022, 08:54 AM   #3
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Quote:
Originally Posted by VickyfromNZ View Post
Recently a mysterious red pipe under the bathroom sink has started leaking. The pipe comes up from the floor, does a u-turn and goes back down to the floor. There is a brass valve at the u-turn. My husband and I thought we had it fixed with some tightening, but then, we we did a black tank flush, there was water all over the floor again. We found a discussion of a similar problem on the internet, relating to a Forest River. They called the part a black tank flush anti-siphon check valve and said it was easy to replace.

Anyone had a similar problem with their Monaco and is the diagnosis right?

Can we get the part on Amazon?

Our pipes have these little metal clamps that look like they're impossible to take off. Do we need to mess with them when replacing the valve?

Thanks!
Your diagnosis is correct.

There are several YouTube videos on how to remove PEX clamps. I use a dremmel tool method. Those clamps are usually in tight spaces with limited working room.

You can get the anti siphon valves on amazon, but don't skimp and get some cheap plastic ones. A leak under that sink going undetected can do a lot of damage. Be sure you get the same size.

If your not sure which one to order, I'd take the old one off and go to a big box or plumbing store.
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Old 06-20-2022, 12:25 PM   #4
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I replaced mine and stinky again in four months. Put a shut off at the hookup and I made up a straight 90.
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Old 06-20-2022, 08:41 PM   #5
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Watts makes about the best anti siphon valve.
Agree a good Watts valve is not cheap but rebuild parts for them are available , decent price . If you can install to lean it toward you should never have to remove it from the piping again for rebuild. Looks like this is go to for RV black flush.
Watts Water Technologies 1/2 LF288A Watts 288A Anti-Siphon Vacuum Breaker 1/2 In., Brass, Lead Free https://a.co/d/3RotuHE
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Old 06-20-2022, 09:22 PM   #6
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I had the exact same problem on my 2004 Monaco La Palma while it was under warranty.

They replaced the valve and it worked great. I decided to never again use the flushouts after that. I've got two toilets and two black tanks.

What year is your Monaco and which model?
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Old 06-21-2022, 10:21 AM   #7
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Thanks, everyone for your replies. Mine is a 2006 La Palma.

I think this MIGHT be a dyi, thanks to everyone's advice.
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Old 07-01-2022, 10:24 AM   #8
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We had this issue, but it was our own fault and there was no real failure to deal with. With a dual valved brass water splitter at the campground spigot, we could turn on water to the black tank flush, the city water, or both at the same time. We found that flushing without turning off the city water feed on the splitter resulted in less water pressure to the check valve, causing it to leak. More specifically, having both valves open on the splitter and simultaneously running any water in the coach caused the pressure at the check valve to drop, and it would leak. Now we always turn off the valve feeding the city water, perform the flush by opening the valve to the flush, then go back to normal when done.
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Old 07-01-2022, 10:38 AM   #9
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Originally Posted by portopa View Post
We had this issue, but it was our own fault and there was no real failure to deal with. With a dual valved brass water splitter at the campground spigot, we could turn on water to the black tank flush, the city water, or both at the same time. We found that flushing without turning off the city water feed on the splitter resulted in less water pressure to the check valve, causing it to leak. More specifically, having both valves open on the splitter and simultaneously running any water in the coach caused the pressure at the check valve to drop, and it would leak. Now we always turn off the valve feeding the city water, perform the flush by opening the valve to the flush, then go back to normal when done.
Yeah, I had leaking issues with mine until I understood how they operate.

You need to have decent water pressure (45+psi), and you need to open the water spigot quickly to force their internal check valve to open.

I thought I'd need to replace mine, but since I started using the system properly, after several years, and many flushes, it works like a charm!
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