I'm no expert, but until recently it was myself, my wife and two teenage daughters. Based on the school of baptism by blockage, here are my thoughts:
1. Too much toilet paper
2. Not enough water
3. Not enough digester
You need to get the blockage removed. Begin by using a clear elbow so you can view your success or failure when dumping. Not gross like you might think. Add several gallons of water and some digester. Let it percolate for a day or so and try dumping again. If the blockage isn't removed the first time, try again until successful.
After you succeed in getting the blockage removed, Start with up to 5 gallons of water in the tank with one digester bottle. Think of this as the beginning to successful tank flushes.
Ask everyone in your trailer to see if they can cut back on the amount of paper used. Human waste is not the enemy and is not causing your tank blockage. The evil villain is toilet paper.
When using the facilities make sure everyone uses PLENTY of water to wash the waste into the tank. You want alot of liquid per a small amount of paper.
I never had issues with dumping the sewer on my old trailer. My Sunset Trail is a different matter altogether. I not only follow the above advice, but I add a packet of digester per person per tank on top of the digester used in the 5 gallons of tank starter. In addition I stole from the geo method (google it) and use calgon water softener with each tank as well. Harder for paper to stick to slippery surfaces.
Of course I use the black tank flush to thoroughly rinse the tank out when done. This combo has worked for me. Your mileage may vary.
Al & Karyl
'08 Sunset Trail ST29RL