What is the best method to remove rust from a gas tank?

Evapo-rust works wonders nothing better then for added protection rinse with water then dry and use some metal etch for about a minute or so available at a auto paint store it will leave a phosphate coating 

I just did mine using Evaporust. Filled with 2 gallons and let it soak for several days. Then I dumped most of it out leaving some for sloshing. I dropped in a half dozen short lengths of link chain that is used for hanging the old fluorescent lamps in your shop. Then I shook the crap out of it for as long as my arms would hold up. Then I took a break and repeated several times. Then I dumped it all out and rinsed the tank with soapy water. Many times. Then I blew it as dry as I could with an air hose. Then I warmed it from the outside with a heat gun to make sure it was dry, then I installed a new petcock and filled it with gas. I don’t use any liner on my tanks. I just top them off so they aren’t exposed to air. I always use an inline filter. Good luck!

Clean it dont line it

Evaporust worked great on my tank.  One thing I learned is if you are starting with a really rusty tank, it is best to remove as much rust as you can before using the evaporust.  My tank was really rusty and I used up a full gallon of evaporust and there was still a lot of rust in the tank. So I used some small gravel and shook it around inside to remove the bulk of the rust and then used a fresh gallon of evaporust to remove the remaining rust.

So if i had to do it again I would start with the small gravel, remove as much rust as possible and then use the evaporust.  This saves some money and you can probably reuse the evaporust as it won’t be fully spent/consumed if removing only a small amount of rust. 

Good luck with your tank!

I've derusted several gas tanks. On 2 tanks ( CT1C and Honda Mini Trail) the rust was very thick. Pin holes developed. I was able to save the original paint but had to line them with 2 coats of POR-15. They are still good after several years.

I wonder if these parts as well as Datsun fenders and hoods were made from compressed rust.

If you have more time than money, white vinegar works like a charm too, Just be ready to let it sit 2-4 weeks depending on how much rust there is. I like to empty the tank after the vinegar, washing it out with water, dry it with air and then spray it down with wd40 to displace any remaining moisture since that's what it was made for. Then blow dry again.

Vinegar will eat through petcock...  use block off plate.

Good point, I use any random piece of wood, drill two holes in it for the bolts and clamp it on.

Because I was going to put a new petcock on anyway, I just left the old frozen one on there. Biggest problem with my tank was it had a thick hard layer of black goo from decades-old leftover gas on the bottom, and up the-side about an inch and a half. I ended up using carburetor cleaner, letting it soak, then blasting it through the filler hole with my pressure washer. I finally got all that out, and as far as rust, there was just a light layer. I let it soak in vinegar for a number of days, rattling nuts and bolts inside. Dumped it out then washed it with soapy water and dried the interior with a heat gun. As soon as it was dry I misted it with WD-40 and made sure it was all coated. In fact I think the black goo kind of saved the bottom of the tank from rusting badly.

It's been running well with a large inline filter, and I haven't had any problems yet, even though there is a little bit of rust leftover. I try to keep the tank as full as possible, and go for a short ride every few days, so gasoline gets splashed around.