DOT requires closeout welding of the fuel tank or filler neck, and any repair work you attempt should only be done by a proficient worker who has done similar serious and sometimes hazardous work before because when cleaning and flushing the fuel system, there may be explosive fumes that can easily ignite during the repair process. When the fuel tank is removed from the vehicle, it cannot be kept at a place where there is fire sparks/ flames, more so in garages with natural gas equipment since the pilot ignition can cause an explosion.