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Author Topic: Gray tank ordor - don't think it's the air admittance valve  (Read 529 times)

mrschwarz

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Gray tank ordor - don't think it's the air admittance valve
« on: August 31, 2017, 09:45:33 AM »
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!
Michael

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kdbgoat

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #1 on: August 31, 2017, 10:06:52 AM »
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.
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Rene T

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #2 on: August 31, 2017, 11:01:37 AM »
 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.
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Gary RV_Wizard

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #3 on: September 01, 2017, 06:54:07 AM »
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
« Last Edit: September 01, 2017, 06:58:25 AM by Gary RV_Wizard »
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mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #4 on: September 01, 2017, 08:06:28 AM »
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.
Michael

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Alfa38User

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #5 on: September 01, 2017, 08:14:20 AM »
MrSchwartz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #6 on: September 01, 2017, 08:18:23 AM »
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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mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #7 on: September 01, 2017, 09:00:51 AM »
MrSchwartz

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


Oops! Forgot all about it!
Michael

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #8 on: September 01, 2017, 09:02:30 AM »
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. :)) :)) :))
Ditto  :))
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mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #9 on: September 01, 2017, 09:12:07 AM »
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.
Michael

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #10 on: September 01, 2017, 10:16:06 AM »
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.

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.
« Last Edit: September 01, 2017, 10:19:33 AM by Rene T »
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mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #11 on: September 01, 2017, 11:24:45 AM »
Sorry. I meant they didn't find anything that could cause the problem. There was water in the trap. It's a head scratcher.
Michael

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Hammster

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #12 on: September 01, 2017, 12:39:15 PM »
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.

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.
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blw2

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #13 on: September 01, 2017, 01:48:52 PM »
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.
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mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #14 on: September 01, 2017, 02:09:13 PM »
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.
Michael

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Hammster

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #15 on: September 01, 2017, 02:24:24 PM »


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

It may not be easy, but it's a great one. We're all looking forward to what it ends up being.
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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #16 on: September 01, 2017, 04:06:29 PM »
I still say, go with the bleach.
Rene & Lucille & co-pilot Buddy
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2011 Chevy Duramax 2500 HD 4X4
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mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #17 on: September 01, 2017, 04:50:16 PM »
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.
Michael

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Gary RV_Wizard

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #18 on: September 01, 2017, 05:32:27 PM »
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.
« Last Edit: September 01, 2017, 05:34:26 PM by Gary RV_Wizard »
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lynnmor

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #19 on: September 01, 2017, 06:57:21 PM »
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?

catblaster

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #20 on: September 01, 2017, 07:38:44 PM »
    If a P trap is installed with its discharge too close to the vertical riser it will become an S trap. S traps are forbidden by most codes because the siphon the water below the traps weir.  Residential toilets have S traps and that is why many gurgle at the end of their flush, they are sucking air because of the siphon. In fact some toilets are branded as siphon jets. That's my thought on  trap siphoning. 
    A mopstring or hair can act as a siphon by the capillary attraction of the water molecules. I have emptied water trapped in containers by using a rope laid across the side and ending below the containers bottom.
   AAV's are not to be installed using any kind of pipe dope since it has shown to get under the sealing disc. I don't understand the mechanism by which it can do that but many manufacturers state that in their literature. You can eliminate AAV being the source of the smell by taping a sandwich bag over it, sealing it tight.
    When you say "sink" are you referring to the sink in the kitchen or the lavatory in the bathroom, lavatories have an integral overflow that bypasses the drain stopper, sometimes these can get really nasty inside with bugs, lizards, mold and just nasty stinky stuff. Running the water down the drain pushes air back up thru the overflow. If you have ever soaped up something really good and then drained it quickly you might notice soap bubbles coming back up and out the overflow. Put you smeller around the overflow opening.....

just a few thoughts
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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #21 on: September 01, 2017, 09:01:19 PM »
Replacing the faucet may indeed make sense.

Some faucets have inside plastic and outside metal. It's possible the wrong plastic was used to make the faucet and causing the stink every time you turned on the faucet. It just seemed like it was stinky gray tank, because it was stinky.

On the other hand, the wrong metal could have been used inside the faucet and it was corroding rapidly causing the stink.

I have actually heard of this problem before from a friend of mine in her sticks and bricks house. One bathroom faucet was stinky when turned on and it wasn't an old faucet. They replaced the faucet with a different brand and the stink went away.
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mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #22 on: September 04, 2017, 09:32:36 AM »
I have more information. After the confusion about the symptoms, we set out on an elimination exercise. Here are the steps and results. We waited two or more hours between steps to make sure we weren't stepping on the results of a test with the previous one.
  • To isolate the drain from the faucet, we poured water from a jug down the drain - no odor
  • To isolate the hot water, we sealed the drains in both sinks and turned on only the hot water - no odor
  • To isolate the cold water, we sealed the drains in both sinks and turned on only the cold water - odor!
  • To see where what part of the cold water line was causing the smell, we sealed the drains in both sinks and ran the cold water in the other sink - odor!
In addition, my wife estimates it take about 3 to 4 seconds for the odor to come out of the faucet after turning the cold water on. To me, this implies that the problem is not in the individual lines feeding the faucets. It appears to be the slider's common cold water hose feeding the sinks' individual cold water hoses. We checked other sinks in the coach and they don't exhibit the problem at all with either hot or cold water.

While we concluded that the problem is the cold water line that feeds the slider, we don't know if it is the hose itself or something growing in it. It's not the whole fresh water system or we would smell it with both hot and cold water everywhere. What's worrisome now is that we ingest water from those sinks and who knows what's in the water? Since the problem is so isolated, I don't think sanitizing the fresh water system is the answer. I'm open to hearing arguments about that, but at this point, it could be that they used the wrong kind of hose for the cold water feed. We have no way of knowing until they physically examine the hose.

We were released from the warranty bay on Friday and are waiting to get into the mechanical bay. Because today is Labor Day, that won't be until tomorrow. First thing in the morning, I plan to see our warranty technicians to let them know about our findings and see what the plan is for remedying it.
Michael

2017 Allegro Bus 45 OPP
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Allison 3000
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Gary RV_Wizard

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #23 on: September 04, 2017, 10:40:14 AM »
Good work!  I'm not really surprised that the odor is on the incoming water. Why worry about which line or what part of the system?  SANITIZE THE WHOLE SYSTEM!  An hour or two of effort and you know that every part is OK, not just the part close to where the odor becomes noticeable.

The odor-causing bacteria are not harmful to humans or pets, just obnoxious. It's basically just sulfur in the water. But the bacteria stick in various nooks and crannies of the plumbing (don't forget the water heater and fresh tank), whether your nose notices them or not. And there is a tiny chance there are other microbes in the system as well.

https://www.rvtrader.com/research/news-reviews/press-room/rv-how-tips-sanitize-your-rv-water-system

https://www.sanidumps.com/sanitizervfreshwatersystem.php
« Last Edit: September 04, 2017, 10:42:45 AM by Gary RV_Wizard »
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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #24 on: September 04, 2017, 04:08:41 PM »
I have seen water hose with some nasty stuff growing inside.  If possible, remove as much hose as possible and install new because the bleach removes very little, it just kills what is there.  With the dead stuff clinging to the hose, it creates a great starting point for new bacteria colonies.  Hose is relatively cheap.

blw2

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #25 on: September 05, 2017, 03:06:24 PM »
yep, good work!

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mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #26 on: September 10, 2017, 08:15:15 AM »
Final post: 44 oz. of Clorox, 24 hours, 2 rinses, new filters. Problem solved, so far. Thanks everyone for your help.
Michael

2017 Allegro Bus 45 OPP
Cummins ISL 450
Allison 3000
Progressive EMS-HW50C Surge Protector
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Rene T

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #27 on: September 10, 2017, 08:51:34 AM »
Final post: 44 oz. of Clorox, 24 hours, 2 rinses, new filters. Problem solved, so far. Thanks everyone for your help.

Can we assume that it was not coming from the faucets but from the drain?
Rene & Lucille & co-pilot Buddy
AKA  Pep N Mem
2011 Chevy Duramax 2500 HD 4X4
2011 Montana High Country 343RL
From the Granite State of NH
& Florida Snowbird in Lakeland FL

mrschwarz

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Re: Gray tank ordor - don't think it's the air admittance valve
« Reply #28 on: September 10, 2017, 02:25:06 PM »
Can we assume that it was not coming from the faucets but from the drain?

That's a safe assumption. I previously posted that we narrowed the smell down to the cold water line in the sinks. This is why we sanitized the fresh water system. The smell was pretty indistinguishable from gray tank smell.
Michael

2017 Allegro Bus 45 OPP
Cummins ISL 450
Allison 3000
Progressive EMS-HW50C Surge Protector
Air Force One

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