2020 Jayco 36FTBS grey water sewer smell in trailer

As was said above I had that problem in my 2012 and could not figure it out then a person at an RV resort told me it could be stagnant water in your hot/cold washer lines so I hooked a hose to each side and ran then for a few a that did the trick;)

All good info! Have been unable to locate vent! Nothing visible under any sinks! Chased pipes into cargo area. One pipe turn up and I think is vent! Nothing visible from roof! Removed cap and odor was slight! Washer dryer is in front of trailer! Odor comes distinctly from kitchen area! Will continue to chase down problem! All replies are welcomed! Together we will solve this
Thanks

Just from personal experience, you may want to make sure the trap for the clothes washer as water in it, if you have one. We recently had an odor that we had difficulty identifying the source. That's what it was. Hope this helps.

I suspect that the tank vent pipe (the pipe that comes down from the roof into the top of the tank) may have slipped down OR is installed to deep into the tank.
The pipe should terminate just inside the top of the tank. If it is installed to deeply into the tank, then once the fluid level covers the end of the pipe it is no longer effective. This is also not good for the tank when dumping as it will cause the tank to crush when draining until the fluid level gets below the vent pipe.
In this situation, what happens when water enters the tank the air has to escape. If the vent pipe is submersed then the air will come out of the admittance valves mentioned above emitting odors into the coach.
Pay attention to exactly when you start to notice the odor. If its before its full, I suspect it is defiantly the tank vent pipe. If so, as long as the top of the tank is accessible its not a difficult fix.

Probably the air admittance valve. Just replace with cheap Home Depot one. The extreme heat and cold in an RV during storage ruins them, cheap or expensive. Tear your old one apart and you will see why. In a house they live an easier life.

Yep look under the sinks and you'll spot a vertical stub sticking up from the drain pipe just after the P trap. Unscrew the valve by hand and replace it. There are better ones, but the one you have is probably $7 from Home Depot.
Link

Maybe the air admittance valve (usually under bathroom sink) is bad.
AA Valve
We put the same chemicals in our grey tank as the black tank in warm weather.