I've had very good luck by cleaning the inside of the tank with hot water & a strong detergent. Once dry, I've used a liquid toilet bowl cleaner to remove the rust. I found that after that process, the tank needs to be recoated on the inside to prevent future rust formation. Most auto radiator shops offer the service.
I hope that helps!
Posted on Jun 19, 2005, 10:46 PM from IP address 184.108.40.206