Quick dissolving toilet paper is a joke. Don't believe me, put the paper you are using in a glass full of water. I'm using Camco RV toilet paper. After letting the glass sit for 1 week, the paper is still whole and did not dissolve at all.
However, when you swish the water around in the glass, then the paper turned into a slurry. So lesson learned, RV toilet paper stuck on a sensor does not dissolve all by itself. It has to be under water for days and then get rinsed off, sloshed around by trailering, etc.
Do the RV toilet paper in a glass test yourself. You will be surprised at what does and doesn't happen.
On a Columbus 320RS, (what I have also) dump the black tank, close valve, fill it up all the way full with black water flush. Then dump it again. Sensors should be clean and read empty. Still no luck, rinse and repeat. When tank is clean and empty, close valve. Then I dump kitchen gray - the handle by the hose hookup. Then I dump shower gray - the 2nd handle in water controls compartment. The shower gray tank is full of soapy water and it will help to flush sewer lines and hose.
When I follow this procedure, the LED lights ALWAYS show empty. I also know that full on the LEDs is not all the way full. So when rinsing black tank, when full LED comes on, I let it keep going for another couple of minutes. I want those sensors cleaned off and the tank fully rinsed.