Water Bottle Bazooka

Step 3 Make the Stopper

While you can use a regular cork for this, I highly recommend using a rubber stopper. The reason for this is that cork will oven have small dents and cracks through which air can leak - a very undesirable thing for a pressure vessel! A #3 or #4 rubber stopper fits perfectly inside the neck of the water bottle (depending on the brand). These can be found for less than a dollar at winemaking supply stores.

I suggest using a Presta valve from an old bicycle tire tube. These are ideal for this application because you can inflate the bottle rocket inside the launch tube, then disconnect from the bike pump without losing pressure. The Presta valve is also long enough to go all the way through the stopper, where a Schraeder valve may not be. Simply cut it off the tube using scissors, leaving about half a centimeter of rubber around the base of the valve.

Select a drill bit that has a diameter slightly smaller than the Presta valve. Install it in the drill press, but DON'T try to drill a hole through the middle of the stopper! Instead, just use the drill press to push the bit through the stopper. Then, remove the bit from the drill press and use the press to push the Presta valve through the stopper where you previously made a hole.

Later on, you may find that the stopper sticks out too far from the neck of the bottle. You'll need to make the stopper a bit narrower. I found that the best way to do this was with a sanding bit on a Dremel (cutting the soft rubber with a knife is almost impossible). Simply use the Dremel to remove thin layers of rubber, until the stopper can be forced far enough into the neck of the bottle.