Options:
1. Fill it up with gas with stabilizer, race gas, or non-ethanol boat gas; pet cock in down position, gas cap locked in place; use block of wood under tank to make level, place in ventilated area on card board or foam
2. Empty gas, let air dry, spray top and bottom inside tank with WD-40;pet cock in down position, gas cap locked in place; use block of wood under tank to make level, place in ventilated area on card board or foam, rinse with fresh gas before use