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Old 09-22-2020, 08:07 AM   #1
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Grey Tank Stink - dumbest thing yet

I've had my 2001 38FDDS for 3 years. It had been lightly used when I bought it. Funny to me is that I am still finding and fixing factory mistakes. One battle I have been fighting is stink in the cabin. It doesn't happen all the time. Sometimes the tanks were near full. Sometimes they were empty. I found that the best thing I could do was put some Clorox down the sink drains before traveling. On our last trip, we decided that the smell was coming from under the kitchen sinks. Today I pulled everything under there apart and I found a grey tank line vent behind the drawers.

My first thoughts are that this is the dumbest thing ever. Dumb because it vents the line inside the cabin. Dumb because it is in a space that can't be easily reached. I'm inclined to fill the cap with sealant and stick it back on top of the pipe. Then I remembered that I am not so smart myself, and thought I should seek advice before I plug this line. I can't think of a reason why I need this vent on my lines from the sink to the Grey tank. What is the knowledge and wisdom of the list?
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Old 09-22-2020, 08:12 AM   #2
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Every drain needs a vent. If you plug it the drain won't work properly. That type vent is designed to let air IN, not OUT. It's likely stuck open if it stinks. You can get them in Home Depot, Lowes, etc. They're very cheap, about $10 or so. Replace it if it stinks.
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Old 09-22-2020, 08:12 AM   #3
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Very common in all types of RVs. It's known as a "cheater vent" by some in the trades. The little rubber flap gets inflexible with age and allows stink to get by. Take it to Home Depot or other hardware store and get a new one and things will work right again.
The above post is just my experience/opinion which is worth exactly what you paid for it.
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Old 09-22-2020, 08:15 AM   #4
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That is called an AAV (Air Admittance Valve). It's there to allow air IN, but not out of the drain pipes. Normal house plumbing will have a vent through the roof behind every drain so that there is no vacuum holding water back. The AAV lets air into the drain line so it will flow out but it's supposed to keep odors in with a flap valve. They are a common failure item and most replace the cheap plastic ones with higher quality.
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Old 09-22-2020, 08:17 AM   #5
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That's a anti-siphon valve.

It stops the water draining out of the sink from pulling all the water out of your pee-traps.

If it isn't sealing, you can get the smells you are experiencing.

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Old 09-22-2020, 08:22 AM   #6
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Just replace it-- any box store.
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Old 09-22-2020, 08:25 AM   #7
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Agree, it’s an AAV since sink drain is not vented to roof needs another way for air to get in.
I would recommend replacing the with an Oates Sure-Vent.
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Old 09-22-2020, 08:26 AM   #8
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Also should flush the tank after replacing the AAV....
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Old 09-22-2020, 08:42 AM   #9
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Go to Home Depot in the plumbing section and you will find the same fitting. DON'T BUY IT! There is a better (read as more expensive) units that you can get. We replaced both of the cheap ones with the Studor and haven't had issues since. I used this one: https://www.homedepot.com/p/STUDOR-1...0341/202275238
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Old 09-22-2020, 12:43 PM   #10
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Good advice from all. Thanks. I went to Home Depot. they had 3 different brands. The cheap one was just like the one in my camper. I bought the $12.99 valve. There was another for $24. I'm guessing the expensive one probably plays music too.

Getting the old valve out and the new one on was a CHORE! I couldn't reach the location through the opening for the kitchen drawers. I had to work through compartment under the sinks. I also had to remove a pipe strap and one of the sink traps to get move the plumbing enough to get to the old valve. It would have been easier if I had been 6'6", weighed 100 pounds, and used to be a contortionist. Now I need a camping test.
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Old 09-22-2020, 12:56 PM   #11
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Open when dumping grey waste tank so water in 'P; traps doesn't get sucked out

Cheap ones used in RVs use a flapper with tang that stretches over time and don't seal
Better ones use spring to close or have cone shaped discs with o-rings vs flat flapper

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Old 09-22-2020, 02:23 PM   #12
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I thought I had a problem with the black tank treatment I was using so I tried several different brands. Like you I would get a smell in the coach SOMETIMES, particularly while traveling. What finally fixed it for me was treating the grey tank also. Now, every time I dump I treat BOTH the black and grey tanks, no more problems! The manufacturer recommends 1 scoop for every 40 gallons. My black tank gets 1 scoop and the grey gets 1/2 scoop. I know this is not to manufacturer’s recommendation but it works for me. If it is very hot or we are out for a long time between dumps I might add another scoop. Try it, it might save you a lot of work.
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Old 09-22-2020, 02:30 PM   #13
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Originally Posted by DrDaveMA View Post
Try it, it might save you a lot of work.
Try IT... you do not mention the name of the product.
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Old 09-22-2020, 04:19 PM   #14
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Was that a screw remove/replace or was it Glued?

Every now and then I lose the seal in the p trap behind the washer/dryer. I just pour some water in the stand pipe, which has no cover.
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grey tank, tank

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