To save you some heartache, try using the search function to locate your answer. What I did was take it to a radiator shop and had it boiled out, but there are much easier ways I am told. Someone mentioned putting marbles in the tank and shaking it to break loose any rust. I'm too lazy for that and it came back very clean from the radiator shop, so I'm happy. I painted the thing with POR 15 when they were done with it and it looks new. I hope this helps.