Swing by your local lawnmower shop and pick up a plastic tank from a riding mower. A gas tank with 20 years of gunk is going to be a bear to get clean......and the mower tank can be hung up on the firewall with enough gas to get all the preliminary stuff finished and even works for a cruise around the block.
When I go to check out a project vehicle I carry the little tank to verify that it was "running when I parked it."
Dave
