Step 11: Launch it
Fill a 2-liter bottle a third or half way with water. Push the bottle on to the bulge on the pipe (a little bit of water will spill--that's ok). Lock the bottle on with the cable ties and big pipe, as explained in step 8, above. If the big pipe does not stay on, line the inside with duct tape as explained at the end of step 8. Hook a bicycle pump to the tire valve. Once you start pressurizing the bottle, you must keep the launcher pointed toward the sky until the bottle has been released. Consider it to be like a loaded gun.Start pumping air. If the pump has a pressure gauge, pump up to 70 psi (5kg/cm) or whatever you can comfortably reach, but not higher. If it starts leaking (and assuming the bottle does not have a hole in it), then you might have to further adjust the trigger but If it is a slow leak, you might actually want to keep it that way because it disarms the launcher if some knucklehead leaves it around pressurized.
With the launcher pointing to the sky, pull the rope...HAVE FUN!