Is the tank metal or plastic? There are several multi-part sealers that work very well on motorcycle tanks and I have seen them used on garden tractor tanks. There are different formulas for plastic and metal tanks as I remember and the metal tank one uses a etch step to remove corrosion from the tank. Some of the Wheel Horse tractors I collect have a cast aluminum 2 piece tanks where the flat bottom is bolted to the casting. There is a gasket but every one of them will leak unless you put the sealant in the tank.
One sealant is called Kreem, it is not cheap but here is a link:
Kreem Fuel Tank Liner - Street Bike - Accessories - Motorcycle Superstore
I have heard people swear by Red-Kote for metal tanks you can get it at O'Reilly Auto parts. More info about Red-Kote is here:
Damon Industries :: Chemical Cleaner Cleaning Custodian Custodial Degreaser Degreasing Deodorant Disinfectant Disinfecting Floor Finish Housekeeping Jan-San Janitor Janitorial Sanitizer Sanitizing Sealer Treatment Wax
Bruce
Bruce