Designer 35RLTS and Jayco Talk...Thanks Frank!!

My gray water tanks (one of them especially) show 1/2 to 3/4's full. I drain them until nothing is left (I allow a lot of time because of the difference of pipe diameter of these tanks.) and the indicators shows 1/2. Black tanks, battery, fresh all read correctly. My next step is to fill the grays intentionally until they are full, then drain them to see if there is something in the tanks to dislodge...or it's the indicator? Any suggestions?