Toilet 'burps'........time to dump black tank
Sink/shower starts to drain slower.....time to dump grey tank(s)
Been using the above 'technique' for years. Lot easier than trying to keep the cheap OEM probes (stud) clean.
And my tanks are clean.......I dump when full, use built in tank flusher and water runs clear thru the clear adapter.
Worrying about the tank level monitor is just not worth my time.
Kinda like the battery 'level' monitor. JUNK
Don't really need either one.