Ever wondered, what is the intended purpose of these holes on the side of a sink drain. Most all lavatory sinks have what’s called an “overflow”. By design it allows water to flow down the drain – in the event the sink were to fill too high – and not over the top & onto the floor.
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In the time it takes bathtubs to fill, people may walk away and become distracted. Thus, the safeguard. In the kitchen sink, the divider between the two standard basins rises lower than the rim, providing overflow protection.
The drain in the second basin also serves as the vent for the first, providing a route for air to escape the drain line.Unless of course the drain was plugged or slow draining but that’s an entirely different story.Some sinks have the overflow hole in the front of the sink – same thing just different design.
Assist with Draining: The holes assist your sink every time you use it, whether you notice them or not. The holes provide an extra opening in the sink to help water drain faster.But how can they be helping if the water has not yet reached the side holes? They help by allowing the air to escape and making sure that the main drain works at its full capacity.