Gray tank ordor - don't think it's the air admittance valve

We just got a new Allegro Bus 45OPP in April. We're in Red Bay getting several warranty issues addressed. One of them is that one of the rear bathroom sink drains emits a gray tank odor when running water in the sink. The tech replaced the air admittance valve, but the problem persists. Here is what I know.

• There are two sinks next to each other in the rear bath.
• The sinks are on a slide.
• Each sink drain has it's own P-trap and air admittance valve.
• After the P-traps and AAVs, both drain lines connect together to a vertical pipe into the floor where I assume it connects to a hose to go to the gray tank.
• One sink doesn't have an odor when water is run in it. The other sink does.
• The smell appears to be coming from the drain. The odor is not stronger under the sink, where the AAV is.
• The odor appears to dissipate after a minute or so of running the water.
• If running the water again in the problem sink within a minute or two, the odor doesn't return.
• After about 15 minutes or so of not running water in the problem sink, the odor returns when the water is turned on again.

 
If it was an air admittance valve leaking air, wouldn't the odor be stronger under the sink with the faulty valve and emanate when either of the sinks was used? To me it seems to be behaving as if there is no water in the P-trap of the problem sink, but I cannot imagine where it is going. Also, if the P-trap was dry, wouldn't running water in any sink force the odor through the dry P-trap?

Could it be a problem with the main gray tank roof vent? We also occasionally get a gray odor from the shower after shutting the water off. The shower drain uses a HEP-VO waterless valve. The tech blew the valve out with compressed air and the odor spread out through the shop, so he doesn't think it's that.

The tech's original solution was to put an odor eliminator solution (Bio-Zyme) in the gray tank to get rid of the smell. I don't think that fixes the problem. It's more of a way to mask it.

Can anyone suggest what might be causing the problem? We're stumped!

When redoing my kitchen sinks years ago, the plumber that was directing me said I shouldn't have a trap for each basin, both should be tied together first, then go to the trap. Don't know if that's true or not, and whether that can be part of your problem.

You could pull down that trap just to make sure there is water in it. If there is, the smell is not coming from the tank. I would pour a 1/2 cup bleach in the drain and let it sit for several hours. Try to make sure the bleach coats the ID of the pipe all the way around.

It is possible that two P-traps close to each other can interfere, such that one drains and ceases to be a trap (an empty trap is just an open pipe).  As I understand it, it's a potential siphon action that can occur if they are different heights relative to each other. That (plus extra expense) is probably why most double sinks share one drain and trap.  Should be easy enough to check to see if each trap retains water, though.

I wonder if one of the new type Hepvo waterless drain traps would solve the problem?

http://www.dyersonline.com/hepvo-1-1-2-waterless-trap.html

Good thought. We are in Red Bay having a bunch of warranty issues addressed. This is one of them, but the technicians seemed to be stumped yesterday, too. They are disassembling the P-trap today. If they don't have success fixing it, I may try a HEP-VO. My former coach, a Winnebago Tour, used them throughout. They take up a lot less room under the sink, too. If the technicians find the problem, I'll report back.

MrSchwartz

Don't forget to update your signature with that new rig information!!!  Congratulations!!

MrSchwartz - I want to commend you for setting such a good example. So many people come in with a question and give us no information to go by, i.e. 'My tank stinks, what is wrong?' and then never report back to us to tell us if any of the suggestions helped. You're being a good forumite. Thank you. ) ) )

Alfa38User said:

MrSchwartz

Don't forget to update your signature with that new rig information!!!  Congratulations!!

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Oops! Forgot all about it!

SeilerBird said:

MrSchwartz - I want to commend you for setting such a good example. So many people come in with a question and give us no information to go by, i.e. 'My tank stinks, what is wrong?' and then never report back to us to tell us if any of the suggestions helped. You're being a good forumite. Thank you. ) ) )

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Ditto  )

One of the techs disassembled the P-trap and didn't find anything, but he did notice that one of the collars that attaches it to the drain pipe was cracked and he replaced it. We though perhaps the crack was big enough to let some air out, but not enough for liquid.

He was working outside on replacing a lamp and I inflated the air bag so he could get his arm under the fender. Another tech working inside commented that he got a pretty strong whiff of gray tank when we did that. Hmmmm.

mrschwarz said:

One of the techs disassembled the P-trap and didn't find anything, but he did notice that one of the collars that attaches it to the drain pipe was cracked and he replaced it. We though perhaps the crack was big enough to let some air out, but not enough for liquid.

He was working outside on replacing a lamp and I inflated the air bag so he could get his arm under the fender. Another tech working inside commented that he got a pretty strong whiff of gray tank when we did that. Hmmmm.

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You said they didn't find anything. I hope there was water in the trap.
You said originally that "The odor is not stronger under the sink" so I wouldn't thing that small crack would have anything to do with the smell . You also said it smells when you run water in that sink. This one is interesting. Hope they find the problem.

Sorry. I meant they didn't find anything that could cause the problem. There was water in the trap. It's a head scratcher.

mrschwarz said:

He was working outside on replacing a lamp and I inflated the air bag so he could get his arm under the fender. Another tech working inside commented that he got a pretty strong whiff of gray tank when we did that. Hmmmm.

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Makes you wonder if the drain line where it attaches to the gray tank, or somewhere along the flexible hose used to connect the sink drains to the tank, has a leak. Inflating the air bag would cause the water in the tank to slosh a little bit, or even just to sort of force air from the tank up that drain line somewhere to a leak.

just thinking out loud but I'm coming back around to the AAV in my thinking.
As I read through I was going to suggest disassembling the under-sink piping and traps to look for "gunk"
but since they did that and found nothing, I'll take that to also mean things were clean.
so
if there's water in the traps you wouldn't get sewer gases backing up
so that leaves the AAV
They are just simple basic diaphragm valves and it wouldn't take much for it to get fouled....so even a new one could be faulty in some way

I had found that mine were a bit less than hand tight from the factory....but the diaphragms were also leaking so i replaced them.

Great thoughts. The smell is definitely coming from the drain in the sink. This was confirmed by my wife and the technician. If it was the AAV, the odor would be stronger under the sink and it's not. Also, the technician replaced ALL the AAVs.

There are two sinks. Each one has it's own P-trap, AAV and drain pipe going down the back of the under-sink cabinet. They join in the middle and go through a single hose into the gray tank. Since the problem is only in one sink, the tech is concentrating on the area before they become common.

Frankly, we're all at a loss. We did, however, discover another cracked coupling ring on the sink that isn't having a problem. He's replacing that and is going to install a new P-trap line in the problem sink. We'll see what happens then.

Sorry I didn't give everyone an easy problem. Thanks everyone for your suggestions.

mrschwarz said:

Sorry I didn't give everyone an easy problem. Thanks everyone for your suggestions.

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It may not be easy, but it's a great one. We're all looking forward to what it ends up being.

I still say, go with the bleach.

Okay. We're out of the service bay and back in our site for the weekend. Tanks are dumped and my supervisor er wife is inspecting. The last thing done was the faucet was replaced. The tech says that another tech said that someone else had the same problem and this is what fixed it. Go figure.

So far, in the past two hours, no smell.

Experience has shown me that the nose is an excellent general detector but not a reliable source locator. The absence of odor underneath is not, I think, conclusive. Maybe by the time you get your head under a sink you have displaced enough air to momentarily push the odor aside? Dunno...

That said, I think Brad makes a good point. If there is water in the traps, then only the AAV is left. Either that, or a broken pipe or fitting.

Another experience I've had is that one sink alone exhibited odor from the water in the faucet. Every time we ran water in that sink, we had a stink. Thought it was the waste drain, but it turned out to be smelly hot water, i.e. a heater tank that needed sanitizing. I cannot explain why only that one faucet released water with a noticeable odor, but that's what it was. Maybe the smelly bacteria had grown more in that particular branch line than the others?  The odor is near identical to gray tank aroma.

Has the pipe to tank connection been checked?  Has the vent pipe thru the roof been checked to see if it is sealed?  Did anyone try temporarily bagging the AAV?