Yes, Biostrip 20 is pretty much perfect for this. It's thick so you can paint it on, it takes about an hour to work. Check out this topic, the guy uses it to just strip the paint off archers bows:
http://www.dakkadakka.com/dakkaforum/posts/list/387259.page#3146907 Just a tip: you might want to varnish the areas that you plan on keeping first. Not that varnish will protect the paint from Biostrip in any way, but when you're done stripping you might want to rinse parts in soapy water, so having the tank varnished would make that bit easier, as you can just rinse the whole thing without having to worry about the paint getting wet.
EDIT: in fact I've got loads, I'd be happy to post you a little jar of it if you
PM me where to send it.