Work it and work it more. While working it keep upward pressure on the tank. I have heard of folks using old piano wire to cut the tank away from the foam.

I used a 12" saws all blade. Tape up end to make a handle and manually saw down edge stringer. Then dig out foam with what ever you can. ( Claw hammer
,prybar , whatever fits) Then just pryout tank. ****ty job but not that hard. where on long island are ya?

i broke the foam up with a saw blade also . then used a ratchet strap hooked to a garage rafter and wrapped around the filler neck to pry it up .

Good ideas but its wedged in good... Will mess around when I get home from work.. Also what can I do with old gas?? (Legally)