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Old 04-11-2019, 08:52 AM   #1
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Stinky stinky Class A motorhomes

Ok, I was asked the other day by a friend of ours about his stinky $175k used moho.... It was a beautiful coach, stunning with all the bells and whistles. BUT every time they would go down the road it would have this "smell"..... you know the one....

First I asked him if his pot would hold water, Yep... Then asked if he filled the P-traps in the plumbing drains, Yep...

He talked about getting tank vent toppers....told them they wouldn't help... HuH???

Ok, here is why!!!!

I have found that most ClassA moho's have a furnace ducting system that a duct that goes into the tank compartment to keep the plumbing and tanks from freezing in the winter. Some even include small fans in this duct to circulate air into this compartment. This sounds like a really good idea..... sort of....here is a surprise, hot air rises!!!

So, when the furnace shuts down at night and the coach cools, the warm stinky air from the tank compartment tends to rise through the tank compartment duct into the furnace duct system thus into the coach. Tank water holds heat too.... It is not sewer gas, but just the smell from the air around the moist plumbing and large 0-ring black pipe tank entries. When driving down the road hot air from the pavement is forced into the tank compartment vents and up the into the furnace ducting. Heat also build up in the tank compartment because of the hot pavement heats the compartment and hot air rises with the smell into the AC cooled people compartment....

Now, some of the moho mans have tried to put duct flappers to prevent this but they are designed to work with furnace fan pressures not 70 mph highway plus cross winds speeds... So, when you are moving you get stinky Class A moho's and when you are stopped you get none. When it is cold out you only get stinky when the furnace cycles off and..... you get the idea....

What to do???? There are several solutions... close off the tank compartment duct and use a incandescent bulb to heat the compartment when ever you are plugged in. How??? stuff a rag in the duct if you can reach it.

Move the flex duct to another compartment or just remove it and insulate the pipes.....

One moho I have uses a huge hole around the shower P-trap to circulate the warm air to the tanks. I had to make a plate to seal this to eliminate the smell. What we need to do is find an alternative to using the furnace to heat the tank compartment. It doesn't take a lot of heat, but a consistent one in subfreezing weather..... Incandescent bulbs either 110v or several 12v dc ones will work.....

SMMS... Stinky Moving Moho Syndrome... stink source has been solved...

I'll leave you with this..... Here is a thought, if the tank compartment is vented outside, could the mice be getting in the vent???? Hmmm... where is the vent??? All good questions in the moho world....
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Old 04-11-2019, 09:13 AM   #2
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A properly sealed and vented black tank should not emit odors into the basement. If it does something else is wrong.
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Old 04-11-2019, 09:24 AM   #3
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Quote:
Originally Posted by spdracr39 View Post
A properly sealed and vented black tank should not emit odors into the basement. If it does something else is wrong.
Agreed, neither my '02 Dutch Star nor present Country Coach have a problem.
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Old 04-11-2019, 09:32 AM   #4
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A properly sealed and vented black tank should not emit odors into the basement. If it does something else is wrong.
What he said ^^^^^^

I would check the vent pipe for obstructions, and the toilet bowl seal for leaks.
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Old 04-11-2019, 10:07 AM   #5
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Quote:
Originally Posted by spdracr39 View Post
A properly sealed and vented black tank should not emit odors into the basement. If it does something else is wrong.
X4 The ONLY connection between the sewer system and outside air should be on the roof.

Nice "engineering" but missing the point.
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Old 04-11-2019, 10:23 AM   #6
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X4 The ONLY connection between the sewer system and outside air should be on the roof.

Nice "engineering" but missing the point.
Yeah, the OP is fixing a symptom, not the problem.
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Old 04-11-2019, 11:09 AM   #7
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When I store the sewer hose in the wet bay, I spray the ends with Lysol and put the end caps on. I then spray the adaptors with lysol. When the door is opened for the next use, it smells fresh. There is no odor coming from the tank area. I have occasionally had a sewer type smell in the coach when one of the Vacuum brakes under the sink is bad, but never from the sewer tanks.
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Old 04-11-2019, 11:35 AM   #8
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I had this problem on a 77 motorhome I had years ago. I found the pipe (in the closet) going to the roof vent from the black tank had NO SOLVENT! Easy fix, but disgusting to find such shoddy assembly.
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Old 04-11-2019, 12:33 PM   #9
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Agree with others that this is not the problem.


I would also question if the smell is actually from the black tank. Given the description and the conditions of when the odor occurs, it may likely be from the grey tank air admittance valves within the coach itself, and there are several, not to mention the washer drain pipe. I had the exact same issue in my Alpine and after changing out all known AAVs, only solved the problem by digging a bit further and finding a hidden AAV for the washer, in addition to the drain pipe. Once that was sealed, odor gone.
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Old 04-11-2019, 02:17 PM   #10
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The 360 roof vents absolutely do work I had a problem on rough roads or multiple RR track crossings creating bad stink 360 installed and problem solved.


Vacuum vent under bathroom sink went bad causing grey tank stink different odder from black tank but still bad.


Black tank stink in a MH is not a normal condition.
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Old 04-11-2019, 04:29 PM   #11
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Non of my 3 MH have any smell of poop.
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Old 04-11-2019, 05:29 PM   #12
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Just buy a different MH. Mine has HydroHot heat in the basement and 3 heat pumps on the roof, no furnace ductwork to leak any smells. Seems like an easy fix......... ;-)
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Old 04-11-2019, 06:25 PM   #13
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Lots of things to check. As previously suggested, check the air admittance valves for the grey water system. However, there are several things to check and you need to work through the whole black and grey plumbing system to find the culprit.

I had this problem and chased lots of things until I finally discovered that there is an anti-siphon valve for the black tank flush system. That valve was bad. Once found it was a simple job to replace it. But I chased a lot, as i turned out for me, of loose ends before I got to the problem.
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Old 04-11-2019, 09:35 PM   #14
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Quote:
Originally Posted by spdracr39 View Post
A properly sealed and vented black tank should not emit odors into the basement. If it does something else is wrong.

Make that X5. A heating vent in the basement will not allow odors to get into the house unless something else is seriously wrong....like a leaking tank.

My guess is it’s the GRAY tank, which can smell as bad or worse than the black! Guess how I know that! ;-)

Also, check all the P-traps, including the washer/dryer.
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