I'v used white vinigar in gas tanks before as well as on other rusted stuff...It works really good but you have to be very careful not to let it sit more than it needs to. Cause the acid in the vinigar will eat the metal too after its done with the rust. Usualy half a day is all thats needed. Then pressure wash. Make sure you get everybit of vinigar out and off of it. Thats a old trick.