I used two gallons of Muratic acid & sloshed for 5 minutes. Poured in two gallons of soda water to kill the acid. Poured it out, rised, let dry & coated with RedKote tank coating. Super easy. Those who have problems with the coating coming off usually didn't prep per instructions. I've used Kreem on the '70 HD & RedKote on the '38 Coupe and have had no trouble with either. I prefer RedKote over Kreem. It seems to flow better when wet and makes a harder coating when dry.
If you don't coat your tank you WILL get rust in your tank eventually. As you drive the gas level drops & is replaced with moisture laden air which immediately starts to rust the bare metal. Refilling the tank does not remove that rust. The rust continues to build over time.
The acid costs about $2 a gallon. Some prefer Phosphoric acid which is more expensive but safer to use. The RedKote is expensive but worth it at about $25 per quart or $75 per gallon.
As the old Fram commercials used to say: "You can pay me now or pay me later".
