The Temple Institute: In-Depth Temple Study: The Cups and Small Holes
 
The Cups and Small Holes: Dimensions

These two silver cups had a type of "nozzle" on the bottom - a small hole for the water and wine to drain through. The opening in the wine cup was wider than that of the water, because wine is thicker than water and flows more slowly. In this way, during the Sukkot festival when the wine and water libations were poured simultaneously, the contents of the two cups were drained at the same time, as halachically required. 
Contents:   Part I,    Part II,    Part III