We have seelevel sensors on our Monaco, I put them in in 2012. Most recently, maybe 2 months, the gray tank sensor says 100 all the time. (when draining it goes to 95 for a bit, then back to 100) T...
Not many replies realize the problem the OP has is with the GRAY WATER TANK.
I was able to install a flush-out in my gray water tank and use a valve to switch between flushing the black water or grey water. It's been working great. The odors from the grey water are often as bad or worse that the black water and I wanted flush both.
I use Happy Camper after a friend recommended it very highly. I can't say all the odors are gone but they're a lot better than they were.