Too much TP and not enough water. When you get home, open the black tank dump valve and stick a garden hose up into the tanks and turn the water in. It is going to be a stinky dirty mess, but you have to get the pule of dry poo out of the tank. Once you have it as clean as you can that way, close the valve and search online for the geo method of tank cleaning. Basically involves adding some water, crushed ice and water softener and then driving around for a while. Hopefully this will break up the remaining poo pile.