The link the Tiny posted is for the proprietary Renu process. I used this a few years ago on my Diamond T, which has no reproduction available. It is pricey compared to buying a new reproduction tank, if it is available.
In a nutshell, this is what they do. First, they cut holes in the tank, about 1 inch in diameter, all over so they can visualize the entire interior. This is especially important when you have baffles, which interfere and defeat attempts to clean a tank yourself. After media blasting the interior they place some sort of plastic material in the interior, and then braise plugs in the holes they created. The tank is heated in an oven. Finally, they coat the exterior with the plastic material and heat the tank again. The tank comes back from them with a black matte finish, not metallic looking.
I did this nearly 15 years ago on my Diamond T and have had no problems. I use a clear plastic filter before the pump and have never had debris in it. I highly recommend this process if you have no other choice. When I did mine I had to ship the tank to California, as no local shop were available. At the time it cost just over $300.
https://www.gastankrenu.com/ You can look for a local shop at this link.
Kent
