Tom, something else that I do is after I dump and close all the valves then add 1/4 cup Dawn and pour in 5 gallons of water. The soapy water slushing around while your traveling will really clean the holding tank. I also have the luxury of having a built in oscillator system in my tanks this cleans my tanks and my sensors. If a person has caked up material they should buy what Ray Chez, suggested in his post. I use an enviromental safe deodorizer for smells.