The magician and a volunteer each have a bottle and a tube. No matter how hard they try as each turns over their tube the magicians bottle is always right side up and the assistants bottle is upside down.
Magically, on the last try, the magician's bottle finally matches the volunteer's bottle, after which the magician can produce a "third" bottle that can be given out as a souvenir.
Manufactured with genuine soda bottles
This is a classic effect updated for the current generation.