water leak under bathroom sink . $70K nightmare

Jeremy888 · 10-26-2018, 04:17 AM

There are 2 white water lines,under the bathroom sink ,(actually only 1 line) connected by a black thingamjig that looks like some kind of pressure relief valve possibly. It is leaking out of the cap on top . What is this? I turned off main water valve and it is still leaking. This 2017 Montana 3950BR 5th wheel is turning into a 70,000$ nightmare HELP. The iwners manual as usual is worthless . Can any one tell me what the maximum water pressure is allowed in these rigs . ?

jkohler70 · 10-26-2018, 04:24 AM

That's the anti-backflow valve for your black tank flush. It's a vacuum breaker. I've only heard of them leaking when using the black tank flush. There's no pressure in that line otherwise. It's a part that is often overlooked during winterizing and cracks. Some have replaced them with a brass valve from the hardware store.

Frank G · 10-26-2018, 04:27 AM

I think that is a anti-siphon valve. For the black tank spray system? For the fresh water system? Others will chime in.

The water system should handle upwards of 75psi. IMHO

Jeremy888 · 10-26-2018, 04:31 AM

OK Thank you ! My flush hose is hooked up, but off Perhaps the valve at the Rv Park connection is leaking i will check it out .

Jeremy888 · 10-26-2018, 04:52 AM

OK , I pulled the black tank flush hose off the RV park spigot and the valve does indeed have a drip leak . There was a pressure build up in the hose. The leak has now stopped . So I can say that since it is leaking with just a drip it is probably leaking also when washing the black tank . I will try that next . So Jkoler70, Your description rings true .So am I correct thinking this is a vacuum operated check valve which prevents the black water ftom backing up into the flush line ? Also what do I ask the hardware store for ? A vaccum breaker check valve? Thank you very much!!!!.. This forum is my owners manual !!!

**JRTJH** · 10-26-2018, 05:48 AM

That "thing" is the black tank flush anti-siphon valve. It is a "notorious leaker" and almost everyone who has one either has experienced a leak or will, in the near future, experience a leak. Many of us just don't use the black tank flush, some of us have replaced the valve when it leaks with another of the same type (it'll leak again, trust me on that) or replaced the valve with either two fittings, eliminating the anti-siphon feature, or with an upgrade, brass anti-siphon valve.

It will not leak unless you're actively running water through the black tank flush system. It is only connected to that 1/2" PEX system. It won't leak so long as you don't use the flush, so just be sure your black tank is full when you dump until you get a replacement. I'd suggest an upgrade brass anti-siphon valve from Lowe's. They're located in the "lawn irrigation" section of the store. Cost, about $20. If you buy a replacement, fragile valve like the one that's leaking, it'll cost about $40, so the "upgrade is cheaper"..... YMMV

ChuckS · 10-26-2018, 05:51 AM

Yep it’s the biggest piece of plastic junk ever.. They will fail.. they will also crack if not blown out with air before freezing temps. Then you have a flood.

Take the valve off and go to Lowe’s or Home Depot and buy a brass replacement valve...

I don’t use mine at all because my blac tank line is flat and level so I wash mine form the sewer connection fitting outside with a Valtera clear fitting and gate valve. Not everyone can get a good flush with they way I do it due to how their black tank drain line runs...

Jeremy888 · 10-26-2018, 05:59 AM

Thank you Chuck S , Well i was going fishing this morning... ...but now I'll be plumbing .. I m going to just replace it as you and Jkoler70 have advised ... I'll follow up when repair complete. Jeremy888

Jeremy888 · 10-26-2018, 06:50 AM

To all, They are mostly 60$+ There is one called an " atmospheric vaccuum breaker " at Lowes for $ 11.37 ..Will this work? see photo . ill needva couple of 1/2 " nipples too.

Steveo57 · 10-26-2018, 07:19 AM

Mine was leaking so I just got rid of it and use a backflow preventer device on my hose connection outside of the trailer.

Jeremy888 · 10-26-2018, 09:12 AM

To: Steve57, Pregnant,(very good!) Idea. And if it leaks its outside the trailer!!! So did you put ir right on the hose bib , or where the hose connects to the trailer? I suppose it would not matter..

Steveo57 · 10-26-2018, 11:15 AM

Quote:

Originally Posted by Jeremy888

To: Steve57, Pregnant,(very good!) Idea. And if it leaks its outside the trailer!!! So did you put ir right on the hose bib , or where the hose connects to the trailer? I suppose it would not matter..

I just leave it permanently connected to the black tank flush trailer connection.

Jeremy888 · 10-26-2018, 01:40 PM

I learned a lot ...fixed as per steve's advice .Used a 1/2 inch 90 elbow and 1" long nipple( plastic drip line fittings) to replace the cheap anti siphon piece of junk. Put the 3/4 " vacuum breaker on the out side flush hose . Tested and proved . Total cost $7.42. Plan to also use the flush fitting on the sewer hose as per John's advice. I need both ways to help me remove " poop mountain " cordially left for me from the previous owner . Thank you to all who helped out here

Ccrew · 11-01-2018, 09:32 AM

Easiest way is to use a shark bite fitting that has a built in check valve and do away with it. It doesn't need a vent, and the valve is normally closed unless the black tank flush is pressurized. $14 or so at Lowes.

itat · 11-01-2018, 09:45 AM

On mine, the previous owner must have had a leak in that plastic vacuum breaker valve because he installed a plastic 90° fitting in its place. I use a simple brass vacuum breaker valve on the end of my dedicated black tank flush hose outside. I'd put one inside it they didn't cost so much but I can't justify the price as a weekend and vacation camper. If I was a full timer I'd be willing to spend a little extra to have it in the line inside.

FlyingAroundRV · 11-01-2018, 12:40 PM

And for your bonus question: How much pressure can the water system take?
Look at the water pump for a sticker that shows its output pressure. Then set your regulator for something near that pressure, not much more. Your plumbing may withstand high pressures from the city mains, but that pressure may cause the non-return valve in the pump to jam. If that happens, you'll have to disassemble the pump to free it.

Jacketsbum · 11-01-2018, 06:51 PM

Ok I'm the ignorant one here. I hook up a hose to flush my black tank, the water sprays into the tank to rinse out whatever. Sometimes I close the waste valve to fill the tank to gather waste not being hit with the spray. Eventually the waste water coming out clears up and I disconnect everything. What vacuum or siphon am I creating? I'm not quite getting this?

**chuckster57** · 11-01-2018, 07:07 PM

Quote:

Originally Posted by Jacketsbum

Ok I'm the ignorant one here. I hook up a hose to flush my black tank, the water sprays into the tank to rinse out whatever. Sometimes I close the waste valve to fill the tank to gather waste not being hit with the spray. Eventually the waste water coming out clears up and I disconnect everything. What vacuum or siphon am I creating? I'm not quite getting this?

The anti siphon valve is installed between the hose connection and the black tank. The valve is installed at a higher elevation than the hose connection, so when you turn on the hose, water has to travel UPHILL to the anti siphon valve, then DOWNHILL to the tank. Inside the valve is a “plug” that lifts and allows water to flow in one direction, and when you turn off the hose and disconnect it falls and allows the water in the line between the valve and hose connection to drain WITHOUT pulling any water from the other side.

This is the quick explanation, hope I explained it enough to answer your question.

Local150 · 11-01-2018, 08:31 PM

Quote:

Originally Posted by jkohler70

That's the anti-backflow valve for your black tank flush. It's a vacuum breaker. I've only heard of them leaking when using the black tank flush. There's no pressure in that line otherwise. It's a part that is often overlooked during winterizing and cracks. Some have replaced them with a brass valve from the hardware store.

When I tried to use my black tank flush I went in side and water was coming out under the bathroom sink. Is that valve likely what caused the water on the floor ? And what's the remedy. That is in advance

jeff57 · 11-02-2018, 05:32 AM

Quote:

Originally Posted by Local150

When I tried to use my black tank flush I went in side and water was coming out under the bathroom sink. Is that valve likely what caused the water on the floor ? And what's the remedy. That is in advance

Mine leaked there too the first time out and the problem was the interior PEX line wasn't securely clamped to the hose connection receptacle on the outside. The remedy was to remove the receptacle from the outside, pull it and the attached PEX line out through the opening then separate and secure the PEX line to the receptacle with a new and better hose clamp. Problem solved.
Hope this helps!

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