Odor from shower drain

[LK23]

We have a new 2017 Dutch Star 4369. We get odors from the shower drain. I suspect it is soapy shower water and possibly hair in the Hepvo valve or the long horizontal drain pipe to the gray water tank. I have removed the shower drain grille and attempted to clean the drain leading to the Hepvo valve, yet still have the odors. So far, the only resolution is to place a cover over the drain screen.

Any suggestions?

This odor is evident at various times of the day and is especially noticeable when running the rear bath exhaust fan since there are no windows to vent fresh air in the rear bath.

[tizzyfit]

"If" it's soapy water and/or hair causing the problem, try pouring boiling water
S L O W L Y down the shower drain. May have to repeat the process a few times to achieve the desired results.

[Algoma]

Sounds as if your Hepvo valve is not doing its job of blocking fumes coming back from the holding tank. I would contact Newmar and get this fixed under warranty.