We have the San-T-Flush so I first make sure I am at least 2/3 full before initial dump. If not, I run water into the tank using the San-T-Flush. Once drained, I use the San-T-Flush to fill the tank back up to 2/3 and dump again. I'll repeat one more time depending on how the water looks after the first rinse.
I then put about 5 gallons of water in the black tank and my wife adds a concoction of Dawn dish soap and Calgon liquid water softener and we leave the campground and let it do the work.
The liquid Calgon is very slippery and helps keep anything from clinging to the sides of the tank. So far it has been working well.
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