The last one I did was "apparently" out of gas but to be on the safe side I tossed a can opener in the heavy plastic (sealable) bag and let it sit for acouple of days then punched a small hole in the can with the opener. It was not out of gas. The bag was instantly filled
with the gas and I barely had time to get the bag into a big cardboard box where I let is sit for several days. Success.