Here are the results of this semester's toilet bowl flushing experiment.

A total of 32 students sent in observations:
The water in 18 toilets was observed to rotate clockwise, counterclockwise spinning was seen in 16 toilets.

Because the Coriolis force does not play a role in determining the direction of the spin of draining water, you would expect to see equal numbers of clockwise and counterclockwise spin.  And that is what the results of our experiment seem to indicate.