It's not necessarily crud hung up on a sensor. It is more likely just the continuity of the water on the side of the tanks. Calgon is a surfactant which reduces the surface tension of water, causing it to be more fluid which will help it slide off the side of the tanks making continuity between sensors less likely. This is really the only part Calgon has to play in the many black tank cleaning recipes.
2016 Rockwood Windjammer 3029W Diamond
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW