Yep ..after the washing with the Dawn and then acid and rinsing with water I dried it and let it sit for several days.
If you saw the inside of this tank when I got it it was BAD and it had a good amount of sludge in it.
Dawn is a great soap to get rid of oil and all kinds of greasy nasty stuff been using that and Fantastic for years removing grime off of just about anything including parts.
My hope was the acid would get rid of the heavy rust, it was flaky inside, and it wouldn't leak and I would run a filter and be done. But after the rust was mostly gone it had 2 pinholes.
I followed the directions that came with the Caswell. I cursed those F'n screws bad!!

It took me some time to get them all out, the stupid tank has a lip inside where the cap is that allowed the screws to get wedged in it.
Its not leaking yet , I keep saying that to myself, but if you look in the tank you can see a couple potato chip size pieces floating and you can see the fuel under the coating where the tank humps up inside for the frame rail.
I will drain it eventually and stick a scope in, AND look for a new tank, their getting a bunch for a good one on E-bay.