Of course the gas tank was rusty from sitting for who knows how long in a shed in western WA. I decide to go the vinegar route first, I've had pretty good luck de-rusting old dirtbike parts in the past and vinegar is so cheap compared to stronger acids. This is the general procedure I followed if you're unfamiliar.
- Fill tank with vinegar and let sit for a few days periodical shaking it to death.
- Drain tank, strain the chunkies out, refill and repeat.
- If its still rusty/crusty, drop a handfull of small metal parts i.e. washers, nuts, BBs.
- Refill with vinegar and continue shaking the shit out of it.
- Repeat until the tank is more or less clean.'
- Rinse with water repeatedly until it comes out clean.
- Drain and rinse with alcohol to get rid of the remaining water.
- Drain and rinse/fill with premix. You want to do this quick because the alcohol will flash rust the bare metal once it dries.
I decided not to coat the tank at this point, seemed like more hassle than its worth for a tank that I intend to keep topped off.
I couldnt get a decent pic of the inside but it looks very clean from what I can see. most importantly, the outlet screen is clear and intact.