I need some schooling on the proper care of the black tank. We "dumped" when we left the last park but I am never sure if we have completely emptied the tank. What is the proper procedure and how do you make sure the tank is completely empty and do you leave SOME water in it with the deodorizer - even in winter? I always dump the "body waste" tank first and then the other one after that. Is there anything more I need to know?