[Ggmac]

If your sending unit is out , I use purple stuff industrial cleaner , just about a 4 oz cupful and a small piece of chain , if no rust a light dog chain works . Let stand after the chain rotation, oh definately leave a section of chain out so you can hold or wire it to a part on the tanks exterior , for about 15 to 30 minutes . Rinse with water a couple of times . If the tank is coated or tinned , dilute the purple stuff abot 50-50 with water . I get my purple stuff from home depot , it is the strongest , ive tried them all . Wear gloves and goggles and dont get any on any painted surface .
Good luck