Originally posted by Camron Rust
You got lucky and owe that credit back to the teacher. 😉
The direction of the swirl is due to the manufacturing geometry of the toilets...not the location of installation.
Thank you for pointing this out -- I'm amazed at the number of people who think that the change is due to the coriolis effect. The effect, while real, is way too weak to be seen in a toilet or a bathtub, unless the water is very still.
See, for example, http://www.snopes.com/science/coriolis.htm