the coriolis force / effecti don't know how we went from installing a digital thermostat to discussing the effect of the coriolis force on the draining water in a sink or a toilet, but we did discuss the matter and agreed further researh was required.
the result is that while the force, caused by the earth’s rotation, is indeed responsible for air being pulled to the right (counterclockwise) in the northern hemisphere and to the left (clockwise) in the southern hemisphere, whose effect is the observed curved path of moving objects relative to the surface of the earth (hurricanes are good examples. they curve to the right in the northern hemisphere and to the left in the southern hemisphere), it is too weak to affect such small bodies of water as contained in a sink or toilet. in fact, one can find both counterclockwise and clockwise flowing drains in both hemispheres.
«be very, very careful what you put into that head,
because you will never, ever get it out.»
~thomas cardinal wolsey (1471-1530)
read this faq for further information on the subject.