Hi Paul, Erica Grow, our Weekend Meteorlogist quickly replied Monday Evening. Thanks for the question.
A: Most of the time, storms in the Northern Hemisphere rotate counter-clockwise. Just the opposite in the Southern Hemisphere, where the rotation is nearly always in a clockwise direction. The rotation is due to the curvature of the Earth, as you might imagine. You've probably heard of the Coriolis parameter; the strength of the Coriolis rotation gets stronger the closer you get to the poles. That's why tropical systems don't strengthen and develop too close to the Equator; there just isn't enough rotation to make it happen.
But, if a system is small enough (and doesn't last very long on a time scale), it is not as strongly affected by Coriolis. A small percentage of Northern Hemisphere tornadoes rotate clockwise because they are much smaller than hurricanes and other storm systems, such as wintertime Nor'Easters.
As far as the water in the drain, I had heard that this was a myth... and a quick internet search confirms that it is a myth. Fill up your sink and see which way the water drains. It's just as likely to drain clockwise as counter-clockwise... it depends on the shape of the sink!
