some other ideas.
Dawn Dish soap works well with cutting grease. Put some in the holding tanks with hot water before departure and let it slosh around in the tanks, rinse and dump at next stop.
Removal of and cleaning the p-traps is easy and fast.
The zip-it is barbed and also would be good for the shower drain.
One other thing to also check periodically is the roof vent and make sure it is free and clear of any debris like bird stuck in there or a old wasp nests. Funny where critters can make there way sometimes.
Lastly, if all else fails, check the actual valves for proper opening and closing.
06 King of the Road 37RLQS
06 Coachman Cross Country 5.9L 300HP 382 DS
03 Jeep Wrangler, 4.0L James, Trina, SMSgt, USAF Ret