I decided to try and clean my coolant overflow tank since I was replacing a battery tray. Couldn't get the inside clean, so I decided to make my own tool. Cut a bunch of strands off an old mop, taped them to a 1/2 drill bit, and used a little steam and Simple Green to loosen things up. Stuck the drill/mop tool in the hole and went to town. Make sure you tape up the drill completely because you will rub on the opening and bottom. Not perfect, but worked better than I expected.