Same thing happens in my RV. At different times, I use the cleaning wand, backflush, various cleaning liquids in the tank, drive around with tank partially full to shake things around, etc. Sometimes I can get the indicator lights to be accurate....for a few days. Then it's back to showing 3/4 full when I just emptied it!
Just get used to how many days you can last before the tank gets full. Sounds like you have a straight visual shot down the toilet. Me too. So I just look down there to check.
I like what Old-Biscuit wrote. Don't let worrying about your tank indicator lights disrupt your camping fun.
