Overflow Drain Sink 📍

When water rises above the primary drain but below the sink rim, it enters the overflow channel (built into the sink’s porcelain or metal) and flows down to join the main drain pipe. This creates an air gap that also helps the sink drain faster by allowing air into the drain system, preventing airlock.

The prevalence of the overflow drain has fluctuated with interior design trends. overflow drain sink

An interesting hydraulic interaction occurs when the main drain is open. As water rushes down the main drain, the airflow from the overflow can create a siphoning effect, slightly increasing the drainage speed of the sink. Conversely, if the overflow is clogged, the sink may drain slower due to "air locking," similar to trying to pour water out of an upside-down soda bottle. When water rises above the primary drain but