It might be old news but I just found this article: http://www.sschapterpsa.com/ramblings/Venting.htm and I thought I'd pass it along.
Originally published in Saltwater Angler
STEP #1; Use a small hollow device like a hypodermic syringe or sharpened basketball inflation needle for a venting tool. Stainless steel is hygienic and resists rust.
STEP #2; With wet hands or a towel, lay the fish flat on top of a cooler or the boat's covering boards. Gently push the pectoral fin flat alongside the fish's body.
STEP #3; The venting area is in the middle of the trailing edge of the fin, in the fatty muscle tissue. Using a slight forward angle, slip the venting tool point under the scales and with moderate pressure, push the point barely inside the body cavity.
STEP #4; You will see the belly deflate and hear the gasses escape after the tool is inside. Take care not to puncture the stomach or intestines if they are protruding. Once the pressure is released, the fish will retract them.
NOTE; Don't use a solid object like an ice pick to vent. The gases won't fully escape and bacteria may be introduced. Rinse the venting tool after use to clean it so that it is ready for the next fish.