In a 23 ft travel trailer for about 6 months and the black water and grey water sensors are stuck at 2/3 for the last month. We tried some of the granular stuff from camping world but didnt do a thing...
They very seldom work. Debris gets on them that is hard to get off. I use dish soap to aid in cleaning them. Doesn't always work! I put the soap in while we are traveling. The sloshing cleans part of the debris off.