Bought a really nice Antares Red 76' tank off Ebay recently. The guy swore it was good to go. It had little rust inside, well what rust was there, was deep, at the weld on the perimeter edge bottom on the lower kickstand side. I rode with that tank for 3 days, no problem. 4th day, I made it to work, but as soon as I shut it down it was pouring out. Got right back on and rode home home 10 miles. Scared the Hell out of me. POR-15 works. I used the complete treatment. That stuff is really hard when it sets up.