Yahoo Message Number: 16938 (http://groups.yahoo.com/neo/groups/Country-Coach-Owners/conversations/messages/16938)
We found that if we emptied too often, waste stuck to the inside of the tank and moved when we did; we had back flushes installed on both the black and gray tanks so that when we did empty, we could wash the inside out very well and then leave some water for a starter. Hope this helps.