Black & Grey tank readings

I've never had any problems with my sensors indicating correct levels. I thoroughly flush my tanks before departing a campground but while at the campground, the dump valves are always closed except when I'm emptying the tanks. A couple of times a year, I use a wand down through the toilet to clean off anything sticking to the walls. I use Happy Campers Holding Tank Treatment and added a flush-out to the grey tank. I also use and prefre Charmin Ultra toilet tissue and have no issues with it. I've been RVing for over 40 years.

Below is a link to a dealer's website where you can learn about the Happy Campers treatment.
https://www.happycampers.store/