As Jane Austen would say, it's a truth universally acknowledged that the Coriolis effect determines the way water moves in a flushed toilet.
Perhaps she wouldn't be discussing toilets, what with Georgian era manners and all that. Point taken. But if Austen were alive today, she'd probably be like the rest of us and assume the Coriolis effect -- which says Earth's rotation affects how we see the movement of certain objects -- influences the direction of our toilet water. The idea is that planetary rotation causes the water to spin clockwise in the Northern Hemisphere, counterclockwise in the Southern.
Of course, you're starting to get the idea -- this is another inaccurate science fact. In reality, the Coriolis effect isn't going to make any difference when the force of the flush is so strong. Even the shape of the bowl needs to be accounted for [source: Scientific American]. Coriolis can noticeably affect giant things in Earth's atmosphere, such as the Gulf Stream, but not smaller phenomena like curveballs or flushing toilets [source: Boyd].