The idea that wayer goes round a plughole in the opposite direction in the 2 hemispheres is a myth. There is a coriolis effect, but it is too weak to have that effect. The direction of draining water is more governed by agitation in the water, often related to the way the basin is filled.

The myth is perpetuated by eterprising people at the equator who "demonstrate" the effect either side of the equator, but who in fact contrive the effect by the way they fill the bowls. Because it has become "common knowledge" and because it is supposedly related to a real effect, science teachers have continued to perpetuate the myth.

This site:

http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html

Explains it better than I can and shows how to fake the effect.

Bagpuss