A French "squatter" toilet in a service station near Toulouse.
(source of this image)
 A free, completely automated self cleaning "Sanisette" toilet now found on the streets of Paris. (source of this image)

Here are the results from the Fall 2015 direction of spin in a flushed toilet experiment.  Thanks to everyone that participated, The response this semester is the highest ever.

CW spin
 CCW spin
Fall 2013
 35
 29
Spring 2014
 24
 17
Fall 2014
 12
 24
Spring 2015
 17
 26
Fall 2015
 41
 33
Totals
 129
 129

The Coriolis force does not play a role in determining the direction of spin in a draining toilet or sink.  On these small size scales, the pressure gradient force is much larger than the Coriolis force.  So we should expect to see roughly equal numbers of counterclockwise and clockwise spinning motions.  You can see for totals of all the data collected during the past 5 semesters, that was true.  The experiment couldn't have turned out better.  I mentioned in class that I might make this my life's work.  With results like these I think it's probably time to move onto something else.