How to remove rust from gas tank. My gas tank is so rusty that the fuel in my clear in lin filter is brown and nasty. I have to change filters once a month. I can drop the tank but don't know the best product to clean it and prevent the rust from coming back. The car was sitting 7 years before getting a new 305 engine put in. I would like to do this as cheaper than a new tank which cost 100.00