An issue of great importance

In New Zealand (and in the Southern Hemisphere generally), the toilets do not "drain in the opposite direction". Mostly they drain straight down, because the Coriolis Effect does not prevail at the scales associated with toilets, and because of the design of the toilets here. From the Wikipedia article on the Coriolis Effect:

The time, space and velocity scales are important in determining the importance of the Coriolis effect. Whether rotation is important in a system can be determined by its Rossby number, which is the ratio of the velocity of a system to the product of the Coriolis parameter, and the lengthscale of the motion:

Ro = {U}/{fL}.

A small Rossby number signifies a system which is strongly affected by rotation, and a large Rossby number signifies a system in which rotation is unimportant. An atmospheric system moving at U = 10m/s occupying a spatial distance of L=1000km, has a Rossby number

Ro = {10}/{10^{-4} * 1000 * 10^3} = 0.1

A man playing catch may throw the ball at U=30m/s in a garden of length L=50m. The Rossby number in this case would be

Ro = {30}/{10^{-4} * 50} = 6000.

Needless to say, one does not worry about which hemisphere one is in when playing catch in the garden. However, an unguided missile obeys exactly the same physics as a baseball, but may travel far enough and be in the air long enough to notice the effect of Coriolis. Long range shells landed close to, but to the right of where they were aimed until this was noted (or left if they were fired in the southern hemisphere, though most were not).

The Rossby number can also tell us about the bathtub. If the lengthscale of the tub is about L=1m, and the water moves towards the drain at about 60cm/s, then the Rossby number is

Ro = {0.6}/{10^{-4} * 1} = 6000.

Thus, the bathtub is, in terms of scales, much like a game of catch, and rotation is likely to be unimportant.

It does mention that if you are very, very careful about your setup, and make sure that there is no latent vorticity in the water, and your water bin is totally flat, and you contrive a plug-and-drain system that can be opened without introducing any new disturbance to the water, then you can fairly reliably get it to drain counter-clockwise in the Northern Hemisphere vs. clockwise in the Southern Hemisphere. But toilets? The effect is overwhelmed by the stink-nuggets that gave you the impetus to use the toilet in the first place, among other factors.

The other thing about toilets here is that most of them offer you two options for flushing. There are two buttons on top of the tank, and some sort of mark or shape on or of them to indicate that one is bigger than the other. Allegedly, they correspond to a greater or lesser flush, which you should choose appropriately depending on what you just put into it. However, my direct experince with this system is that each button initiates a flush of more or less equal volume and force. In the toilets at work, the buttons seem to be physically linked, so that pressing one or the other causes both to depress. At home, the story seems to be the same, but you can pretty easily moderate the flush by holding the button for more or less time.

Still, the toilets here provide plenty of opportunity for Demolition Man-inspired three seashell jokes, further buttressing my belief that that movie is the most terrifying and prophetic vision of the future that Hollywood has yet produced. Two words, bitches: President Schwarzenegger. Those two words should give you ample reason to test out whatever flushing mechanism you may have on your nearest toilet.