Gray and Black tank sensor issue

Planecrazy; I think there are a lot of good suggestions mentioned here to solve your problem but if you're like me and prefer to make the sensors work like they're supposed to you might try what I've been doing for years and 6 rvs. Since my gray water tank is totally inaccessible for flushing, I put about a quarter cup of tsp powder that has been dissolved in water and about the same amount of Calgon water softener powder into the gray water tank and then fill the rest of the tank with water, let it sit at least over night drain in the morning and you're good to go. The black water tank is usually accessible through the top of the bowl and that is where I put a water powered wand in and blast the bowl and the sensors. Keep in mind where the sensor are located and concentrate on water blasting that area. I've done this for over 25 years and it has always worked for me.