For this project you will need the following: PVC pipe (a 10' length of 3/4" was used here), a "T" connector (sized to match the PVC), duct tape, a vacuum, some newspaper, and any ball that will fit inside the PVC (in this case, paintballs).
Step 2: Assemble
Tape the vacuum hose to the middle opening of the "T" connector and push the connector onto one end of the PVC. There, that was pretty easy.
Step 3: Try it out
Put the ball in the end of the PVC that doesn't have the connector on it. Cap the ends of the PVC with newspaper; you may need a buddy for this part. Turn on the vacuum and the newspaper should stick to the ends; a vacuum should be created inside the PVC. Now, aim at something not alive, or that could possibly get damaged, and pull the newspaper off of the end that you loaded. The ball will shoot out the other side with impressive speed.