Grey tank odor, but only when starting

[redrhinino]

2014 Tiffin Phaeton.

Every time when we start heading down the road, we get a strong (unpleasant) smell. We both think it reminds us of onions, but that's the nearest we can get to describing it.

Once we have been driving an hour, we seem to lose the smell. We can park, everything is good. Stay parked for several days, no issues. Start the rig up, start driving, ONIONS AGAIN!! I do have 2 vent connections on the top of the rig, but they have Tees on them, so its hard to tell if they are ok.

Sometimes we have the same faint smell if we have been out of the coach all day, but it usually is not there. I have tried doing multiple things to clean the tank, but still the smell comes back. (It does seem to be coming from the kitchen sink area.)

I'm trying to figure out what the heck is going on that we get the smell so strong when we start driving.

Anybody have any ideas? I considered changing the Hepvo valve, but it only really smells when we start driving, and I don't want to start shotgunning parts at it..

[Old-Biscuit]

HevpO valves usually do not allow odors back inside from grey waste tank

Got a Sink Stopper.
Close sink drains with stopper and see if you still Smell anything


With HevpO I suspect no Air Admittance Valves are used so that should not be the fail point...unless MFG did install them (not normally used with waterless traps)

[Leonandlisa]

So I would check for air admittance valves under the fixtures, maybe loose or failing. Do you have roof vents open when traveling? If you do, that could create a suction that could draw air out of a dry trap or a failing AAV.

I don’t know why it only happens in the beginning, unless you become accustomed to it after awhile.