Recently, after a bunch of reading about this, I used POR-15 Fuel Tank Sealer. (They make other stuff also). I think this is a moisture-curing polyurethane product. My report is so-far-so-good. It seems to cure very hard and so far–but I have only a few weeks to go on–it seems to be resistant to typical 10% ethanol motor gas.

People are also using it for sealing cork floats.

One suggestion based on my experience: The stuff is loaded with metallic pigment. I presume aluminum. Shaking is not enough to mix this–it needs to be stirred with a bottom-scraping action. I didn’t realize this, not supposing that a tank liner product would be pigmented. When I got to the bottom of the can it was very thick and gloppy.

There are two-part products around that might have a higher performance.

Yup – Por 15 works great. It’s expensive, and you must follow the directions, but it will seal all the leaks. I used it on my 1947 Sportsman built-in tank back in February and no leaks to date.

I just resealed a couple of 6 gal tanks. It went like this: (1) pint of acetone sloshed around and left for a couple of days. (2) hot water, stones, and TSP sloshed around. (3) phosphoric acid etch. (4) tank sealer. quite a pain, actually, and I doubt any tank coating will work without effective cleaning down to bare metal.

Then, add cleaning up and painting the outside of the tank, and the various little springs and O rings and gaskets that may need attention, and the cork gauge float, and the inlet screen, and the gasket in the filler cap which likely is shot …….