pipe and tank treatment.
I had read in a trailer magazine that if you add 2 cups of water softener, like White King, to a gallon of water and then pour into your drains, plastic sinks, and toilet bowl it will make the surface slippery and less likely for debris or grease to stick to it also if added at the start of the season as ot sloshs around the holding tanks it does the same for them. I have done this every time I have drained the holding tanks or at the start of the season and I think it has worked. When I drain the gray water it seems gray and not to have had any of the black oily discharge when I first bought it.