Step 1: Materials
1. Pump (any air pump will do)
2. Ball pin (one that fits your pump)
3. Soda/Water Bottle
4. Stand (For the bottle)
Details about the stand in step 2...
Step 2: The Stand
Step 3: Final Remarks
1. The cork must be tightly inserted into the bottle (air tight)
2. When pumping, you may hear some air escaping the cork. This is normal. As long as you keep pumping all should work
3. Position the rocket AWAY from yourself or you will be hit by half a litre (weighs 0.5kg) flying at about 5 meters per second, which will hurt.
4. Pumping lasts for about 40 seconds.
Have fun and be careful.