* The Coriolis effect is too weak to significantly influence the direction of water draining from a sink on the equator. The Coriolis force is strongest at the poles and weakens significantly as you get closer to the equator. The rotation of the Earth simply isn't strong enough at the equator to create a noticeable spin in a small amount of water in a sink.
* Other factors are more influential: The shape of the sink, the way the water enters the drain, and even a slight imperfection in the sink itself are much stronger factors determining the direction of the swirl.
In short, the Coriolis effect doesn't really play a role in the direction of sink water at the equator.
