Was talking with McNoob (on this forum) at the marina and apparently he had a problem with goo in the tank and was able to clean it by removing the fittings, draining the tank and pressure washing the inside of the tank, sucking out the dirty water and goo with a shop vac and when it was clean, forced air dried it. If it were to work for you that would be faster and a lot cheaper than 25 gals of gas, $50.00 dollars worth of Seafoam and a lot of bad road driving and truck fuel. I forgot to ask him if he used some sort of flex shaft for the pressure washer. Perhaps you could do both with one shot of gas and Seafoam at the end after drying the tank. .