[RayChez1]

Since your coach was a used motor home when you purchased it, it might have been modified by the previous owner. I know of several that have been modified to where IF the grey tank fills up first that it will spill over to the black tank. You might have such a system, but for sure they did not come out of the factory like that.

Now as to the sensors not giving an accurate reading it is because the grey tank gets just as much crud on the inside of the tank as the black tank. So the only way that I solved that problem was to pour into the tank some Happy Camper. It is an enzyme that eats up all the crud on the inside of the tanks and leaves them clean where the sensors will work every time. Mine have been very accurate since I started using that stuff. I discovered Happy Camper at a FMCA rally and buy it through Amazon all the time. It turns all solids back into water and when you dump there is very little smell IF any. RVers that do not believe on using anything but water, when they dump, they just about run everybody out of the RV park with the stink.