Every scientist whom I found any articles on the Coriolis not affecting small masses of water use their own (faulty) notions of how they believe it would work as proof rather than any studies..
I can not say that I know for a fact what is true, but I recognize faulty logic when I hear it. The notion that the "effect is too small to affect small things" logic is about as good as the "any creature living at such a depth must be huge to be able to stand the immense waterpreassure" theory presented in 20000 leagues.. a smaller funnel gets a smaller effect from the Coriolis, sure, but a smaller funnel also means that there is less weight of water that needs to be affected. Ofcourse a "water jet" can make a difference (toilets flushing, or if you leave your faucet on)
I have tried the following experiment in most drains in my current appartment, in my last appartment, and in my parents house; close the drain, fill up sink/bathtub with some water, open it again, and when there is a visible "water funnel" I drip a small drop of candy coloring in to the side of the funnel.. clockwise every time. I live in sweden, and I assume that closer to the equator it would be more likely the results might be irradic.
Well, there is *something* to the myth. If all other factors were equal, it is likely that the water would swirl one way on the Northern and another way on the Southern hemisphere. However, in most cases, other factors will be far more dominant. Water jets being angled a certain way would be a very dominant factor. The shape of the sink and any initial motion could also be very important.
Oh, and if your country is on the equator, your sink will still probably be primarily on either the Northern or Southern hemisphere. The equator is a line, you know. It doesn't cover any area.