both tanks are pretty full and the truck does run. I was told that I could use up the fuel till its about empty, add some sort of additive to it, and fill up the tanks half way hoping that'll losen up the deposits in the bottom of the tank and take care of the sour gas problem. I can't really tell if it smells real bad but I walk by the truck and I smell it without the truck running. I want to avoid dropping the tanks if at all possible.