Drill a half inch hole into the center of the plug.
Pvc air cannon sprinkler valve.
If you have the correct size tap for the nipple you should go ahead and tap the hole out.
Pvc air cannon with sprinkler valve there are a number of cool things you can do with them remote detonation and sentry gun to name a couple not even counting the ease of use that a simple electric trigger has over a rubber powered ball valve as on my air rifle which has to be reset after each shot.
How to build an air cannon with a sprinkler valve.
This cannon is capable of shooting projectiles such as oranges or parts of a potato very far distances and at very high velocities.
A safe alternative for a new style sprinkler valve air cannon trigger.
This instructable will teach you how to build an air cannon that can be triggered with a switch.
It looks awesome and can kill a watermelon from.
The ball valve trigger has since been replaced with a valve from a sprinkler system giving this high power pvc air cannon a fancy brass trigger.