Im still amazed more people dont just invest in the Tornado rinser.($35) I have the clear Camco adapter so I can see what's coming out of the tanks. I can empty my black tank completely and then hook the tornado up and you would not believe how much TP still comes out! More than when the tank was emptying itself.
I run the tornado for 5-10min and make sure EVERYTHING coming out is clear and water only.
The fact is....unless you rinse the tank really well, you WILL have TP hung up on those sensors. I have the least expensive FR model ever and have not once had an issue with tank sensors.