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Old 12-20-2010, 02:22 PM   #1
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Country Coach Owners Club
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Weird black tank odor problem

We have a 2006 CC Inspire 360 that has a serious odor problem only under certain conditions. Flushing the toilet (electronic type) by itself is not a problem and there is relatively no odor, but have either of our 2 roof vent fans on, and LOOKOUT! It is awful. It seems that the negative pressure in the coach pulls the black tank odor directly up into the bathroom and beyond. We had a 5th wheel before and with the exhaust fan blowing out, never had that problem.

Does anyone know of a way to prevent this from happening? A lot of times it is nice to have the vent fan(s) on (which by the way, only exhaust out), but if they are on you cannot flush the toilet without the odor.

Someone suggested that the black tank vent may be blocked, but in my mind, that does not make sense since an open vent would assist in air being drawn through the tank. I am stumped.

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Old 12-20-2010, 03:04 PM   #2
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Being new to RV's the two times it's happened to me I added more deodorant mix and it cured the problem actually the first time I had cheap stuff the RV dealer gave me when I bought the thing and the second time I just did not put in enough as it got towards the full mark with the better stuff I got from the 2nd RV dealer who cured my first time problem. Once I put more of the better stuff in the problem was cured until I was able to dump.

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Old 12-20-2010, 03:13 PM   #3
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Hi arrowheadbob,

I have had this concern on my coach (different make and model)
I found the problem was caused by a poor seal on the ball valve (Sealand toilet) Mine had a slow leak that was evident when the bowl was full of water. It would take a while, but the water leaked out of the bowl and into the black tank. With the bowl empty when the fan was turned on, it would draw odor out of the black tank through the leaking seal. I was able to temporarily repair mine with CLR calcium remover.

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Old 12-20-2010, 03:43 PM   #4
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It seems pretty obvious to me that if you are pushing air OUT, the negative pressure WILL pull air IN wherever it can ...and an open commode flush valve is as good as an open window in that regard. And if the tank vent were blocked, it would be LESS likely to allow air to be drawn up through the commode. You can try to cover the sewer gas with chemical smells, scents, aromas, etc, but if that is the only other opening when you are running 1 or more exhaust vents, the vent(s) WILL pull air in through that opening.

We never run our vent fans w/o having a source of air for them to pull from. I can hear a big difference in the drag on the fan motors when they are trying to push air out w/o having air coming in somewhere. If we have multiple vents open, at least one of them will be turned off so air can come in there while air is going out the others. (None of our Fantastic Fans are reversible models, but I altered them a few months ago so they are now all three reversible.)
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Old 12-20-2010, 03:50 PM   #5
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I found the only way to keep the smell from wafting out of the tank while flushing is to NOT have the overhead vent fan on. For just the few seconds it takes to flush, it's worth it not to smell the "tank perfume" by turning off the vent fan. Luckily, our bath fan switch is just an arm's length away from the throne - easy to reach.

Commenting on the negative air pressure statement you made, our coach addresses that with this sticker. It's located on the Splendide, but I'd think it would pertain to anything that would exhaust inside air. We always have a window cracked open if any exaust fan (bath, salon, stove or dryer) is running.

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Old 12-20-2010, 07:26 PM   #6
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Talking Weather seals are working...

Sounds like everything that seals the inside from the outside is in wonderfull condition.

Flush the toilet to get it full of water and test the fan, if no bubbles or odor then let it get dry, flush with water off or switch off power mid flush.

Retest fan, of odor then souce is confirmed.

Next, find a window to leave open.
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Old 12-20-2010, 07:44 PM   #7
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I had the same problem in the bathroom when traveling and found it to be the rubber flap on the plumbing under the sink was stuck down and wasnt working. I unscrewed this off of the sink plumbing and worked the rubber flap loose and screwed it back on and the sewage oder problem we had from time to time for months was gone and has not returned.
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Old 12-21-2010, 07:33 AM   #8
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What you are experiencing is normal. The toilet is a direct drop to the holding tank and when you have Fantastic fans running, it will pull the odor from the tank. Having a window cracked may lesson the odor, or just turn off the fans.

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Old 12-26-2010, 08:45 PM   #9
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Thank you all very much for the replies, especially during the Holiday season.
Sounds like I will need to keep a window open or turn off the bathroom fan when occupied. I guess we never had this issue in the fifth wheel because it was probably not so tightly sealed as the motorhome.

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