I have fixed my tank monitors. Might not work for everyone. Squeamish might want to stop reading here ;-)
Purchased used motorhome and monitors were unreliable. Tried all the normal things...still not reliable.
Then started driving home after camping trips with full tank and emptying when we got home. No more problems with false readings. We never empty at the campground always drive to the next campground or home before emptying.
All the sloshing around gets everything all blended....sort of looks like a brown smoothy when it comes out. Don't even have to use a tank sprayer to clean the tank unless we are going to let it set for a number of months.
So if things come out chunky that is the problem.....need to make a smoothy.
If you are parked in one spot for the season this solution will not work for you.