Radiator shops will clean them, typically with an ultrasonic tank nowadays…does an amazing job. If it’s badly pitted inside, consider a new one.
I don’t trust those has tank sealers…seen too many fail, and it’s pretty much a one-way street with those things.
A few years back I bought an E Type and the tank was bad, rusty, with holes and dirty. Hot tanked at the rad shop, sand blasted, welded bigger holes, soldered smaller holes, sandblasted again, putty and paint. Looked like new and still going. Did not coat the inside. Compressed air and vacuumed the inside. Little money and lots of time at that time!
Assuming one could get the insides sufficiently cleaned and de-rusted might hot dip galvanizing be an option? I believe it’s bad for a diesel tank, but I don’t think it’s known to cause issues with gas. It must be spotless though or it can flake off.
Interesting question. I don’t know the answer, but I do know that anything that is going to be galvanized needs to be designed to drain the excess completely and rapidly. If you get any pooling or accumulation, it forms crystals that will absorb moisture forever, and cause corrosion.
When I had all my Land Rover bits galvanized at a local, family-owned galvanizing shop, the owner spent about 10-15 mins with me, going over how LR had specifically designed all the parts for the galvanizing process, by showing me all the strategically located drain holes.
It was a fascinating bit of insight, and he was very impressed at how they had done their designs.
You want to be careful welding a gas tank did you fill it with water you can go 
. Jim
Buy a new tank……
Bump
I lived to tell about it! No, did not fill it with water. That’s where hot tanking at the rad shop came in handy!
Hi Erica,
At least with the S3 E Type Fuel Tanks sold by SNGB, they are galvanized.
Brent
same with series 1 and 2 now…
I laughed so hard at your post I pee’d myself.
My solution was similar to John North’s but I hooked it to a low speed motor on a pulley and filled the tank with a collection of nuts and bolts. The noise was amazing. 