Sounds like the very same problem we have...our toilet has a pipe that runs sideways at an angle and into the holding tank. I think paper and solids get stuck in that pipe and don't actually make it to the holding tank. I have a clear tube at the end of the sewer hose so I can see whats coming out when dumping, and the last time we dumped after the weekend I saw no paper or other solids coming out - even though we did the black water flush (cha-cha-cha)- so now I'm worried. I put 5 gallons of water down the toilet along with a blue drop-in that helps dissolve, and some boraxo. I hope this solves our problem the next time we head out - maybe it will solve your problem too. I'm taking a yardstick just in case. Seeing as we will be out for 17 days I'm a little concerned.