I'd say mine work about half the time. :-) Lots of water is certainly the key to keeping tanks clean. When I'm packing up I always run a bunch of water into the black and gray tanks before dumping. Usually I'll turn off the HW heater and run hot water into the gray tank. Also cools it off so I can pull the plug on it. (I drain my HW heater between camps. I know you don't have to, but I do.) At the same time, run water into the black tank until it has a bunch. Dump black, then gray. Refill the black with at LEAST two bowls of water with treatment chemicals. I use this:
https://www.amazon.com/Kronen-KHT003...eywords=Kronen