I learned quickly to not trust sensors. My tank is under pass side bed with water pump and strainer. I use a big light against tank to see actual level. You can run down some and refill. Pumps do not like running dry. I think they do not get sensors spaced properly.
My black tank said 2/3 full last time I cleaned it. Turned pump off, looked down commode and saw tank bottom dry.
As you go along, you will learn what to trust and what to double check.
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