whats the best way to get old varnish out of a tank?

I am a total do it yourself guy, including ring and pinions and automatics. I try and not let anything get in my way.........but that gas tank did.

I tried several options. Eventually after messing around for a month with filters and plugged lines etc. I took it in, had it boiled and I just let them coat it while there.

It seemed like it was $80ish or so. I have not had a problem since and I really, really wished I would have just did it to begin with.

ROB