FIRST THINGS FIRST
WELCOME TO THE FORUM!!!!
Don't trust em.
We do clean them but, we are more interested in cleaning the tanks than the sensors. We use Calgon (for laundry) for this. Calgon only in the gray and galley tanks. Sometimes add a bit of bleach and laundry detergent in the black tank for cleaning. That is all, if it cleans the sensors, cool, if not, oh, well.
Richfaa discovered the lock washer thingy I believe, so far as I remember, that is working for him.
You can hear the toilet when it is getting near full, sound when you flush changes.
As far as the galley and gray, well, sometimes they get us, and they back up. We try to dump the gray after 3 showers, or 3 yorkie bathes. The galley, depends on how much cooking and cleaning we are doing, and that is sorta a guess.
One of the gals, just said she keeps a calendar with dump dates on it. Very organized gal!
Some dump every day, not a bad plan either.