we use 2 cups of calgon liquid water softener ever time we empty the tank and every time we leave on the extended drive we also add about 7 gallons of water with a 1/4 cup of laundry soap...yep we have bubbles by the time we get to our camp spot but we also have a very clean and slick black tank that helps when we are cleaning the tank during our campground stays. We also have a "magic" wand for cleaning the tank of the dreaded pile! It will take a little bit of time, but lots of water will help to soften everything up.