Unless it's leaking slowly, which that one seems to be, it should be able to just hang out for as long as you let it. It's also possible that it managed to blow its burst disk if it was overfilled in the heat.
wow, your tank should still be full. Put a few drops of oil around the burst disk and valve and see if you can see any bubbles comming out of it(Thats bad), or just take it to your local PBstore and have them check it out. Hope this helps
Soapy water...it bubbles more and you can spot the leak easier.
What I'd do now that it's empty is put a drop of oil on the pin valve and then push it open a few times with a screw driver or hex key or something so the oil will get into the valve a little. Make sure it's empty first or it'll just spit the oil everywhere.