h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

You're quoting a fallacy. While the hemisphere does affect which way flow turns in large length scales in the atmosphere and ocean, on the scales of a drain, the turning force from the Coriolis force of the turning of the Earth is too small to make a difference compared to what the water is already doing and the forces due to the shape of the drain (and bath tub/sink etc the drain is fitted in.)

http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html for one of the better layperson's debunkings of this.

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On a separate note...
Take a teaspoon and lower it, near the far edge of the cup, into a reasonably still cup of tea so that half the bowl is submerged and the remainder is out of the tea, with the concave side facing you (that's the side which can hold sugar). Then (fairly slowly) draw the spoon towards you - you get two vortices spinning of the sides of the bowl of the spoon, which follow the edge of the cup around to behind the spoon and dissipate. And the reason for that is post-graduate level fluid dynamics.

AEndr
Middle Atmosphere Dynamicist