Take your clean empty bottles, and fill one 2/3 full of water. Place the other bottle (empty) on to the coupler, or use duct-tape to connect the bottles together. Your done! Its a rather brain-dead process which anyone can do, but there is some technique to it as well.
To Make the Tornado:
- Quickly invert the lower bottle (full) to the top, and with a smooth circular motion, rotate the top bottle (full) to make the tornado.