I had the fortune/misfortune to walk in on a conversation yesterday regarding toilet flushing in New Zealand. A friend of mine is getting ready to take a trip to this beautiful nation in the Southern Hemisphere and he had been informed by his parents that the dunnies flush in the opposite direction Down Under.
This is probably one of the most popular myths of physics. It is an alleged result of the Coriolis Force, an artifact of the Earth's rotation that affects weather patterns. It causes wind patterns "above" the equator to tend toward clockwise spin and those "below," counterclockwise. But it only affects large-scale weather patterns. It's affects are totally negligible in your household drains. The direction of toilet flush has everything to do with the subtle shape of the bowl and various other minute details of fluid mechanics. Oddly, this myth is perpetuated by many science teachers, who ought to know better.
So don't believe what you hear. Credulous world travelers will assure you that every toilet they flushed in Australia flushed backwards. Like other anecdotal evidence, it's nothing more than coincidence.