Drill two 1⁄8-inch-diameter holes into the thick part of the inlet elbow (A). Insert screw eyes.
Attach the 10-foot-long PVC pipe to the elbow's 3-inch opening (B) in line with the 2-inch one. Don't reduce the barrel length—it provides range and velocity.
Attach the 18-inch-long pipe to the other 3-inch opening (C) on the inlet elbow. This is the Wiffle ball–loading tube.
Center the assembled pipes on the sawhorses and rotate them so the loading tube is vertical. Attach bungee cords from the sawhorses to the screw eyes to hold the loading tube in place.
Insert one end of the 4-inch-long pipe into the 2-inch hole (D) on the inlet elbow. Align its other end with the leaf-blower nozzle and use duct tape to securely seal the connection.
Turn on the leaf blower, insert the Wiffle balls in the loading tube, and watch them shoot out! You can elevate the barrel with wood blocks to fine tune your pitch for the strike zone.