What do you mean by vent
The panther uses a back pressure tank to fire. Said system has a valve in each tank that holds the air in. When the gun is fired, the valve is sucked back by a loss of pressure behind it. "Venting" the tank refers to pulling the trigger to create that initial loss in pressure.
A homemade blast button like Buff's?http://nerfhaven.com/forums/index.php?showtopic=21352&st=0&p=301302&hl=+qfd%20+blast%20+button&fromsearch=1&#entry301302