I have a copper sink in the bathroom and because it doesn't have an overflow, the water drains very slowly. It is not too much of a problem, because as the sink begins to fill, it drains more quickly due to gravity, but as it drains down, the rate slows down dramatically.
But my kitchen sink (as most kitchen sinks) also doesn't have an overflow, but doesn't have the same problem. How come? Is it because kitchen sinks have a larger drain?