After enjoying FHU in Texas, I spent my last night, before reaching home, in a state park with only Electric hook up. I filled my fresh water tank half way, ( 2 lights ). Before leaving in the morning, I ran half the tank into my grey, through the sink, and the other into the toilet by holding down the flush peddle. When I went to dump, both my grey and my black got a nice rinsing. Now I don't need to be concerned about my low point drains until winterizing.
Bob