Fill it with Coka cola and leave it overnight
There is no such thing as a "good Coca-Cola". Crap company.Thanks for the replies, gents. I hate to waste good Coca-Cola (I'm guessing it's the phosphoric acid that does the work) so I think I'll start with the vinegar. I've done a lot of electrolysis rust removal for parts and it works well but I can imagine it would be more difficult in a tank. Plus there's all of the gunk the process leaves that would have to be cleaned out.