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Holding Tank Odor, Version 2019
You’ve heard this before, this time it was us!
While traveling this year (2019) we noticed holding tank odor when the coach was closed up and the Fantastic Fan above the shower was started. We narrowed down the origin of the odor to generally the water closet. This happened numerous times and the odor could be minimized by also turning on the water closet fan. Not eliminated just minimized. Finally found the time recently to try a chase down the source. After searching PC for similar experiences we found that the air admittance valve behind the cabinet in the water closet was allowing the gray water holding tank to vent into the water closet.
We were able to actually test this by closing up the coach, ensuring that all drains were closed and then turning on the Fantastic Fan on exhaust. We waited a couple minutes and then used an lighted incense stick to verify that in fact there was holding tank air coming into the coach through the originally installed air admittance valve behind the cabinet in the water closet. We replaced the originally installed air admittance valve with a new one from Home Depot.
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7 Replies
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Just had to replace mine for the same reason. Knew it had to be the Studer vent – just had to find it. Behind the drawer in the bath vanity.
There is also one under the kitchen sink – but a prior owner removed it and glued in a length of clear tubing that presumably exits the floor of the coach. Probably got frustrated with unreliable vents.
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Air admittance valves are rarely allowed for use due to most plumbing codes in the nation. They are usually allowed in places such as in a kitchen when it has an island with a sink, and usually then after a battle with a plumbing inspector.
But I cannot think of an alternative is such an instance.
Our coaches use them because none would likely meet a typical plumbing code and in some instances their use is a matter of convenience for the converter.
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Another source of “stink”’can come from an improper or failed seal/caulking at roof top vents. Pop off the vent cap, and I bet the caulking is dried out or not present. This has happened two different busses by two different converters
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My county allows one per house. Most people know them as “Island vents”. Agree with Jon – with a little work, both sinks could have been vented to the roof.
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I’ll be checking the caulking around those roof top vents. Thanks for the suggestion.
Just an F.Y.I. Our coach has a total of 4 air admittance valves. One behind the cabinet in the water closet (replaced) and one under every sink. The ones under the sinks are very easy to get to.
Thanks all
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The reason most plumbing codes prohibit air admittance valves is because they are prone to failure, whereas a conventional vent stack in a plumbing system has no moving parts and except for a bird’s nest on the top of the stack nothing can go wrong.
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The source of your problem sent me on another investigative tour of our bus. I spent several months when we first purchased our bus in March of 2008 opening and investigating every nook and cranny of the whole coach.
We have developed an odor problem when the bus A/C is running and I slow down for a traffic signal. If the tanks are completely empty, there is no smell, but if they have even one day’s use, then the odor begins as soon as I bring the bus to a stop or near stop with the bus A/C running.
Also, last week we started smelling wet clothes while parked. To be fair, when we are in tent revival, I have wet clothes hanging in the bathroom drying out all the time, but this was excessive.
We have a small corner sink in the commode room and I had removed the panel in the back of that cabinet 11 years ago, but I did not take any pictures or notes. I removed it today and there was the culprit, an air admittance valve. I removed it, purchased a replacement and installed the new one.
We came in from church tonight and no smell of wet clothes.
Maybe this will take care of the bus A/C pulling in holding tank odors too. I will find out in a week or two.
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