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I do not have an answer. However, I will be watching to see what folks may say. My motorhome has never had this issue until this past weekend. We had some low hanging tree branching run across the roof pretty good, and I later noticed the cap was not off slightly. I climbed up and snapped it back on, but have had the sewer smeel ever since.

With the caps on as they were supposed to be, and freshly dumped and rinsed grey and black holding tanks, I am hoping that when we go to use our motorhome next weekend, that I do not have these odors.

So, I am open to any feedback, as well.

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Welcome to the FMCA Forum.

You are on the right track. The goal is to isolate the tanks and their vent system from the interior. Trying to make the tank contents smell good won't work.

Start by checking places that the tanks can vent to the interior:

1. Make sure all "P" traps under sinks, shower, etc have water in them. they evaporate when the coach is not in use and water sloshes out of them while driving. Same for toilet-- keep water in it.

2. Smell under sinks to determine if the check/vent valves are not functioning properly. There should be no smell from them. The rubber check valves do dry out and need replacement.

3. NEVER flush the toilet with the vent fan on, as the negative pressure WILL suck tank air inside.

4. Minimize negative pressure inside while driving-- don't leave roof vents open and depending on design some side window also create negative pressure.

Once a year it is a good idea to take a hose up on the roof (if safe to do so) and run a little water down the vent pipes to make sure nothing is obstructing free flow to the roof. There are several good brands of roof vent caps that create a venturi effect to lower pressure in the tank.

If the smell persists, check for cracked tank, tank fitting, plumbing fitting, vent pipe that has slipped down into the tank, etc.

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Guest Wayne77590

As Brett said. Keep water in toilet bowl and traps. In the traps, for longer periods of storage, put a 1/4 cup of vegetable oil in the drain as a last measure. Vegetable oil will stay on top of the water in the drain and will not evaporate quickly.

For the toilet, if it does not hold water, fill a zip-lock back 1/3 full and place it in the toilet against the ball. It will help in keeping the smell "down." You can do this while on the road, and if you need to use the facilities, pick up the zip-lock and put it in the waste basket until needed again. Just a simple work around until you can resolve why the toilet is not holding water - if that is the problem.

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The previous replies just about cover it with one exception, no one has mentioned a washing machine. This is frequently a source of odor for us. If it hasn't been used for some time, the drain can go dry. Sometimes I think it isn't dry until we drive and then because it is low the remaining water sloshes out of the trap which opens a direct route to the gray water tank. Any dry drain will allow odors from the gray or black water tank to enter the motor home. A gray water tank can smell as bad as a black water tank. Check all your drains for dry traps.

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Great information, thanks.

I was lucky that no foul odors were in my coach, until I started driving.

I cured it by closing all drains and putting a flat rubber stopper on the shower drain. That helped some - finally cured it by putting a plastic baggie over the vents under both bath and kitchen sinks.

Always something, isn't it? ;*)

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Great information, thanks.

I was lucky that no foul odors were in my coach, until I started driving.

I cured it by closing all drains and putting a flat rubber stopper on the shower drain. That helped some - finally cured it by putting a plastic baggie over the vents under both bath and kitchen sinks.

Always something, isn't it? ;*)

Jack,

I am glad you found a solution to your odor problem, BUT, water in the P traps should isolate the tank at the sinks and shower. And the siphon breaks (under sink "vents") are not expensive to replace. The rubber gaskets in them DO dry out or get "crudded up".

Add a venturi-style roof vent cover and you should not need to do anything special to keep your coach sweet smelling.

Brett Wolfe

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