Looks better than new. What did you clean off the spout with. Looks good.
And how do you acid etch the inside with muriatic acid? Is this something where you just pour it in and shake it around?
That's all ya gotta do. You can find muriatic acid any place that has pool supplies.
Pour in a quart or so, MAKE SURE THE RUBBER SEAL ON THE CAP IS IN GOOD CONDITION AND SEALS THE VENT HOLE! If there's no seal, bad things can happen.
(sorry about the caps, but I can't stress this one enough) And don't forget the eye protection!
Shake it up and let it sit upright for a minute or two, then lay it on one side for a minute, and then the other side for a minute, then the front, the back, and the top. After you empty out the acid, pour in a quart or so of white vinnegar and shake well. This will neutralize the acid and stop it from eating all the way through the can. after the vinnegar rinse, let it sit in the sun with the cap off to dry it out and apply your inside coating.
If you follow the instructions on the coating product, you'll have a storage container that'll last a good long time, but you still can't sell it in California, several other states or the city of Dallas.