I had one of my factory black tank flushers clog. It was after my wife spent 2 months in it recovering from knee surgery... A long story as to why for another time and place.
I drilled it out and no problems since.
My sensors have always worked well for us in several TTs. But normal use for us is driving home at least 120 miles, and several miles of rugged dirt roads when leaving camp.
As you experienced, I see no solids to speak of when dumping. I am of the belief that many always dump at the campground, and solids don't get dissolved, and end up accumulating in the tank.
The campground dump station may be real convenient, but it may well be a source of tank/sensor problems.
