I've tried to find the write up on my 240's tank refurb without luck so here goes from my fuzzy memory.
Things you need:
1 gallon muriatic acid, $10
1 quart Denatured Alcohol, $10 I believe?
2 pound baking soda. $1 from a Dollar Store, $.50 each.
4 five gallon buckets
some bungee cords with hooks.
a funnel, with the long stem cut off
quart of Red-Kote
My process: tape up the vent lines out of the tank. Get a rubber cap for the big fill hole.
fill one bucket with 2 pounds baking soda and 4 gallons of water, set aside
pour in the gallon of acid, slosh around for 5 minutes then dump into an empty 5 gallon bucket
pour in the baking soda and water, slosh around for a couple of minutes then empty that into another bucket
pour in the quart of alcohol, slosh around for a couple of minutes pour into a smaller bucket. this will dry the water/soda rinse and prevent flash rusting.
pour in the Red-Kote. Rotate the tank in all directions completely covering the inside.
hang tank with bungee cords, there's some small holes around the edge for the hooks on the bungees. Let the excess drip out into another bucket.
open all vent holes and the fill hole. set it out in the direct sun for 30 minutes, rotating the tank in all directions so it'll set up without pooling in the low spots.
I put my leaf blower in the fill hole and let it blow on half throttle for at least 30 minutes.
leave it in the sun as much as you can bringing it in at night then back out the next day. let it sit for a couple of weeks until the smell has dissipated. this will give you time to get all the evap hoses together for installation of the tank and the evap lines
I poured the soda and water bucket together with the acid bucket then poured that onto all the ant beds in my yard. No more ants!
This is a quick stroll back in time so most likely forgot something. If I remember anything else I'll let you know.
Most important thing was to have everything readily available as this is a time sensitive process if you want it right without flash rust. Leave your phone's ringer off too.
These were good reads before the job, lets you know what to expect.