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Old 06-20-2016, 09:47 PM   #1
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Smell of sewer while driving

We moved up from our 5th wheel this year to a class A, this is our first motor home. We just came back from our second trip in it and although it was just an over niter it was great. However the camp ground didn't have a dump station so we left and would just look for one on the way. while driving there was a terrible sewer smell every time you would either slow down or take off. If you stopped for any length of time it would be gone in minutes. after we dumped it went away naturally but I don't think you should get that smell in the coach? Any ideas it is a 2008 Southwind 37c

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Old 06-20-2016, 10:25 PM   #2
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look at the vent on the roof for your sewer system... see if there is a weather vane type of device on that vent.... if there is one there... and its stuck into the wind your moving air down that vent into the tank and every time you flush your toilet gas comes up... or the seal is bad, and gas comes up.... if that vane is stuck... all you need to do is un-stick it... or replace it...

If your vent doesn't have that weather vane... the top of the vent could be damaged so that air is forced down that pipe....

those weather vane devices when they work... work as a venturi... air blowing by that vane draws up the gases.... sucked up... so to speak...

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Old 06-20-2016, 11:06 PM   #3
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Make sure the bathroom vent fan isn't open and make sure the toilet is holding water. No water in the toilet equals a nauseating "bouquet au bum" in the coach.
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Old 06-20-2016, 11:16 PM   #4
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Oatey 1-1/2 in. ABS PTC In-Line Cheater Vent-39012 - The Home Depot This is your problem it is located under your bathroom sink they just unscrew some are different size either 1 1/4 or 1 /12 in.
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Old 06-20-2016, 11:20 PM   #5
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Had the same problem when traveling with liquid in the black tank ,upon checking I found the vent pipe had some brown stains around it cleaned it up and resealed it. Problem solved
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Old 06-20-2016, 11:38 PM   #6
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I close all vents and run the dash ac on fresh not recirc.
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Old 06-21-2016, 07:58 AM   #7
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Many times, smells from the gray tank can be just as bad as black tank smells so don't automatically assume it is your black tank.

Close all roof vents and windows when driving. Make sure you have water in all of the sink traps including the washing machine if you have one. If you still have smells, check below the sinks for AAV (air admittance valves) and make sure they are working.
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Old 06-21-2016, 08:20 AM   #8
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I had the same problem. After researching all of the fixes available out their I went with the 360 vent cap. No moving parts and works moving or standing still. I check all the other things first like leaky toilet, grey water smells from dry p traps etc. This worked for me.
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Old 06-21-2016, 08:41 AM   #9
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Originally Posted by mccrob View Post
Had the same problem when traveling with liquid in the black tank ,upon checking I found the vent pipe had some brown stains around it cleaned it up and resealed it. Problem solved
If you are finding brown stains around you roof vent pipe I would recommend dumping a bit sooner...
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Old 06-21-2016, 08:50 AM   #10
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Had this with both a class C and A. I believe it's a combination of air flow, to and from the ALL the tanks, and through the tank roof vents and normal air flow through the RV from front to back, exacerbated by windows, air ingress past body gaps and possibly the dash AC. I never did completely get rid of the problem.
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Old 06-21-2016, 08:55 AM   #11
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randy, put some deodorant in the grey water tank.
when you dump, sometimes the water in the kitchen p trap gets siphoned out. leaving an open tube to vent gases into the living quarters. same goes for the bath sink, and shower drain. either fill the p traps or add deodorant, or do both.
febreeze will take care of the odor inside the coach until you can get it vented out.
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Old 06-21-2016, 09:12 AM   #12
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Like some have stated don't assume its the black tank. If my gray tank is not empty I will get a bit of odor. I now always make sure there is a bit of water in the tank as well as add a gray tank deodorizer. Never had an issue with the black.
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Old 06-21-2016, 09:56 AM   #13
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I had the same problem with my Winnebago. Assumed a leak and filled each tank separately with water. The black water tank leaked where the vent pipe entered. It had never been sealed and was loose! The joint was nearly inaccessible, through a quarter-inch gap around the pipe through a steel plate. I cleaned the area with swabs and poured a quantity of liquid epoxy through the gap onto the joint. No problem since then. I hope your problem is easier to fix.
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Old 06-21-2016, 10:27 AM   #14
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As you can see by the posts here it could be a lot of different things. I would not rule any of them out but start with the simple stuff and work from there.
I had the issue and ended up being the grey water tank creating the smell. Had wife drive while I was in the bathroom. At one point air came up thru the sink drain and squirted some ptrap water up at me. Problem was I had half or more of grey water in the tank. When driving that stuff slushes around creating a vacuum or pressure in the tank which removes the water from your ptraps as well as letting sewer gas blowby. Just needed to make sure the grey tank is not to full when driving. On that trip I just refilled the drains and put the drain stop on all the sinks until I was able to dump.

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