We have a 2006 Excursion 39J. The black water tank has two levels. The first, right under the toilet, is about 12" wide and then steps (or drops) down to a lower level that is about 4 to 5" below the first. The problem is that solid waste and paper builds up on the upper level and does not move to the lower level causing a backup into the vertical pipe to the toilet. Even with the built-in water flush turned on full, these clogs will not move unless I put a flushing pipe down into the tank thru the toilet. Does anyone have a solution? This problem is most challenging when we sit in one place for a longer period of time. Out on the road, a partial tank will slosh around and wash this out. Help! I am tired of unclogging a 1/4 full tank.