Anti-Siphon Vacuum Breaker

[dalford]

Is it possible for the Antisiphon Vacuum Breaker to fail in such a way to allow black tank odor into my RV.

I just returned from a 5+ week trip where I was at a park with no sewer hookup thus I had my tanks dumped once a week via a honey wagon. I have not used the black tank flush at all. When I brought my RV home after a few days in the warm Florida sun I had a very strong sewer odor, stronger than I have ever had before. It was coming from under the bathroom sink.

I suspected the air admittance valve but the spare I had was the wrong thread to replace it. So to see if I could isolate the odor I placed a ziplock bag over it and sealed it tight with a large rubber band. No luck, still odor from under sink.

I then noticed the anti-siphon vacuum breaker. I tapped on it a bit and then decided to run some water thru it. The valve did not leak but the odor went away.

I don’t know how these things work but can they fail in a manner to allow sewer gas to escape under the sink but not leak when being used?

[bubbles]

Well, here's the way it is supposed to be installed:

[dalford]

Originally Posted by bubbles

Well, here's the way it is supposed to be installed:

Thanks, it is installed correctly. My question is can it fail in a manner to allow sewer gas to escape into RV ..

[emm-dee]

If it failed any odor that went through it should exhaust through the port where one would hook a hose to do the flush. If you camped for five weeks and didn’t use the tank flush I believe you have a pretty nasty black tank by now. The smells will go up the vent pipe and disburse in many directions.

[dalford]

Originally Posted by emm-dee

If it failed any odor that went through it should exhaust through the port where one would hook a hose to do the flush. If you camped for five weeks and didn’t use the tank flush I believe you have a pretty nasty black tank by now. The smells will go up the vent pipe and disburse in many directions.

Under the sink?

I still have not flushed but just ran water thru flush system and odor went away..

[bubbles]

Originally Posted by dalford

I don’t know how these things work but can they fail in a manner to allow sewer gas to escape under the sink but not leak when being used?

The way it works is: A disk seals off the input side when water pressure is removed and opens to the main valve cavity when pressure is applied. The output side has a spring loaded check (ball) valve that opens when the cavity has pressure and closes when pressure is removed. The valve cavity is open to ambient to break vacuum for the disk to open (sealing off the opening to ambient) and also to allow the disk to close off the input side as the water in the cavity drains out of the input port and associated tubing. Can the check valve hang open and the use of the bathroom exhaust fan draw black tank odors? I suppose anything is possible. I have not had any sewer odor come from my vacuum breaker/check valve.

[5picker]

bubbles described how the valve works perfectly.
Could it leak gases?... sure but pretty uncommon.
BUT, you proved it can. By running water through it and thus eliminating the odor, I'd say you found your culprit.

[Witch Doctor]

Originally Posted by 5picker

bubbles described how the valve works perfectly.
Could it leak gases?... sure but pretty uncommon.
BUT, you proved it can. By running water through it and thus eliminating the odor, I'd say you found your culprit.

If it is leaking, why wouldn't the water being leaking to, I'm confused, which is easy to do, it is a closed valve, there is no outlet like for a hose bib. So how can you get smell without seeing water?

[TitanMike]

Most holding tank chemicals have a line in their instructions suggesting that MORE of their chemical be added as a filled tank "ages" or if weather is particularly hot. I't could be possible for the anti-siphon device on your flush hookup to bleed odor and it doesn't take much to raise a big stink.

Check you tank chemical and see what they instruct. Because it's possible for a treated tank to still contribute odor from the actual chemical itself, pick an aroma you can tolerate and try to dump/flush your tank more often.

BTW, don't overlook the gray tank. They can sometimes be just as foul as a black tank. If it's been warm or you've been on the road it's possible that there isn't enough water in the sink P-trap to block odors. It's a good idea to use some chemical in the gray tank, especially one that helps keep grease and soap buildup under control. Also minimize food scraps that go down the kitchen sink with a fine strainer available from Walmart, HD, Lowes, actually just about anywhere that sells housewares. The food scraps can "compost" and if you've ever turned over a compost pile it smells just as bad as a pile of manure until it's fully composted.

[Ale_Brewer]

My bet is the odor is coming from your gray tank and the p-trap for the bathroom sink went dry.

[cavie]

Originally Posted by Ale_Brewer

My bet is the odor is coming from your gray tank and the p-trap for the bathroom sink went dry.

[dalford]

Originally Posted by Ale_Brewer

My bet is the odor is coming from your gray tank and the p-trap for the bathroom sink went dry.

Not from sink drain. The odor was from under the sink cabinet. I had just returned from 5 weeks camping so the unit had not sit long enough to dry out plus I had just cleaned the sink a few days before. There was water in the trap for sure.

The smell happened rather quickly though. I first suspected the air admittance valve and the one I had purchased as a spare was the wrong sex thread so I covered it with a zip lock bab and used a rubber band to seal off. No effect. I then noticed the anti-siphon valve. I had not used it for a couple of months. The place I stayed for the past 6 weeks did not have sewer connection and I was pumped out weekly by a Honey wagon. I hooked up a hose to the flush out and ran water thru it for a few minutes. The odor went away This this post about could it leak sewer smell into the air under the cabinet?

I have ordered a replacement anti-siphon valve and will install it next time I’m getting ready for a trip. I will let you know if I have anymore issues as the next trip will be over 2 months long. Florida west to AZ, north to Glacier NP, West to Rushmore plus all site in between.

Thanks for the suggestions.