One of the best ways to clean up the insides of a tank prior to coating is to take a couple of pounds of galvanized roofing nails and load them onto the tank after duct taping off all of the openings except the main one, then duct tape that opening as well, then shake, rattle and roll the tank until you are exhausted then do it some more!! It's a good idea to have some friends over for a tank shake party. When you do it long enough you will find the interior of the tank looks shiny new when you empty the tank. Then comes time to coat the tank, I like Red Kote but Cream is a good product as well...