The way that the water in your toilet swirls is determined by
the way that your toilet is built, not which hemisphere you live
in. The toilet shoots the water into the bowl at an angle, which
determines which way the water swirls. What you may have been
thinking of, though, is the way that water swirls when it drains
out of your sink or bathtub. Old science textbooks did say that
this is different in the Northern vs. Southern hemispheres.
Unfortunately, this is one of the many cases where you can't
always believe what you read. The reason that the old books gave
is the Coriolis effect, which has to do with the way that the
Earth rotates out from under something that moves freely. (You
can picture this by imagining a cannon that sits on the equator
and fires straight North. As the planet rotates out from under
it, the cannonball will appear to veer to the right, or go
clockwise. If the same cannon were to be fired straight South,
the ball would still appear to veer to the right, but it would
be moving counterc