Well depending how dirty your tank is Buy one gallon of muratic acid from the pool cleaning section at Home Depot, thats if your tank is extremely dirty or if you have rust in there from decomposed fuel left over time. I actually did this method on a Mustang II Helped my dad out a lot. But that acid can be very expensive like $50 a gallon. The common route get the acetone and pour it in drained the tank,put 1 gal of acetone in it and sloshed it around,do the same 2 more times.then shine a flashlight inside tank,to make sure it was clean. then filled tank with soapy water 3 or 4 times,sloshing it around . then turn tank upside down,drained and flushed tank with clean water. after draining as much water from tank as possible,i left the tank in the sun,with the cap off until it dried. worked great. hope this works