Adding water after dumping black tank

I put a couple gallons in both the gray and black to help keep the seals on the dump valve moist and to help any remaining food particals or waste from drying out. The black tank also gets about a cup of cheap powder detergent and a cap full of water softner. I leave all this in the tanks and on my next trip to the campground, it sloshes around and coats the tank along with breaking down anything during the sitting period.