Start firing tennis balls with the 'weird' but perfect size for such activity. The fit is a bit tight but it makes a good seal on the ball.
Yes, it is just regular old run-o-the-mill SCH40 PVC pipe, but at 2 1/2in (2.46in actual bore) pipe size, just isn't available most places. Will REALLY chuck a tennis ball. You can alsu use with spuds but they would have to be big baker spuds. Use pipe fittings to get the size up or down to 'regular' 2 or 3" pipe
The optional adapters come attached to the barrels. The bushing is the same size as 3in pipe and needs a 3in coupler to attach to 3in pipe.