Michael Palin did North Pole to South Pole travel show. In Kenya he was in town that had the equator running through it. Guides there put match sticks in a tub of water and let it drain north, south and precisely ON the equator. The water swirled as predicted by Coriolis and went straight down when on the equator. Nothing like a bit of empirical knowledge.
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.