Club 80-90 Forums

I'd like to give our grey water tank a clean out, because i'm sure that there has to be some old soap scum, and other nasty cling-on's (Klingons) in there. I've read about putting a solution of water and laundry detergent into it, also pouring in a few bottles of the cheapest coke i can find. Both say to leave it in and to drive around a bit to wash down sides.
Just wondering can anyone back up these claims as being good, or suggest something that they have used?