Waste valves are tremendous when working, but stinky when not.
There are chemicals out there that have coconut oil in them and they have kept my waste valves in good working order on 4 different RV's.
I use 2 times the chemical that the direction call for, but you can never have too much of a GOOD, thing.
Another thing, like the toilet seals, all seals, valves ,work better, last longer when kept wet/moist, use enough anti-freeze when winterizing in tanks to get to valves.
A couple extra bucks, but sure beats working on sewer pipes.
Hope this info helps.