http://www.physics.ohio-state.edu/~dvandom/Edu/newcor.html
[snip] Under extremely controlled conditions, this can cause water to flow out of a container counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere, but your kitchen sink is not so controlled. Things like leftover spin from filling the sink (even when the water looks still, it’s rotating slowly for a long time after it seems to stop), irregularities in the construction of the basin, convection currents if the water is warmer or colder than the basin, and so forth, can affect the direction water goes down the sink. [end]
[ add “sleight of hand” to the list ]
http://www.maztravel.com/maz/explain/coriolis.html
[snip] We’ve all heard the stories about cruise ship passengers who sail south of the equator and report that after crossing the equator the water started going down the bathtub drain in the opposite direction from the northern hemisphere. There have even been TV stories on this phenomena, with (I must say gullible) reporters led down the garden path by “pseudo scientists.” ... w is 2 * 3.14 / (24*60*60) = .000072 revolutions (actually radians) per second, and water drains at around 1 foot per second, so the acceleration of the water is about .000072 feet per second per second. At that rate it would take almost a minute (47 seconds) for the water to be deflected one inch. In comparison to the other forces at work in a draining bathtub, this is almost insignificant, and no experiment that you could do on a cruise ship or in your bathtub could detect a force of this magnitude. The water near the drain is already gone in a matter of a second or less, so there just isn’t any time for a force of this magnitude to do any real work on the water. This effect has been demonstrated under laboratory conditions... [end]