Some teachers around the world, sometime give bad explanation also when talk about the Coriolis force. One of popular bad example is when teachers said: "The water in a sink (or toilet) rotates one way as it drains in the northern hemisphere and the other way in the southern hemisphere. Called the Coriolis Effect, it is caused by the rotation of the Earth."
As I mentioned above, the Coriolis force appears as an effect of earth rotation, while the earth rotation is very slow, only one rotation per day. On the other hand, the water in a sink might make a rotation in a few seconds and so have a rotation rate ten thousand times higher than that of the Earth. It should not be surprising, therefore, to learn that the Coriolis force is orders of magnitude smaller than any of the forces involved in these everyday spinning things. The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore. Actually, the direction of rotation of a draining sink is determined by the way it was filled, or by vortices introduced while washing. So, have no relationship with Coriolis force and of course earth rotation.
I found one good and clear description about Coriolis force at the book I am reading now: The Oceans by Ellen J. Prager (FYI: I never finish read this book, because I only read this book when in train or bus).
In this book she ilustrated the Coriolis force by writing a funny story about a war on drugs where a US soldier has to fire a missile from Washington DC to Columbia. The missile is launched, however it lands not in Columbia but on one of small islands in the Galapagos Archipelago, 500 miles west of South America. Numerous endangered tortoises and much of their fragile habitat are annihilated, environmental groups vigorously protest at the White House and Ecuadorian officials are enraged. The US takes quick action to fire the soldier. Much to his chagrin and embarrassment, the soldier realizes his mistake: he forgot to program the missile guidance system to adjust for the Coriolis effect.
After that, the story continued by explaining in detail the Coriolis force. Better you buy the book or, may be, you can borrow it from me after I finish read it, but I am not sure when I'll finish read this book. You know, I am a lazy man! :)