Empty out two 2-liter soda bottles, and rinse them out completely with water.
Fill one of the soda bottles halfway full of water. Leave the second soda bottle empty.
Add 5 drops of food coloring into the water-filled soda bottle. Select any color of food coloring that you prefer.
Wipe off the openings of both soda bottles with a dry washcloth to remove any moisture.
Place the empty soda bottle opening on top of the water-filled soda bottle opening. Wrap duct tape tightly around the openings where the two bottles are connected. Rub your hand around the taped area to ensure the area is tightly sealed.
Turn the connected bottles upside down to watch the colored water transform into a whirling tornado.