At first glance, the small hole near the top of a bathroom sink looks purely decorative—or even pointless. Many people clean around it without ever stopping to wonder why it’s there at all. Yet this tiny opening plays a surprisingly important role in both safety and functionality.
The image highlights this often-overlooked feature, commonly circled in red, to draw attention to something most of us use every day without understanding.
What Is This Small Hole Called?
That small opening is known as the sink overflow hole (or overflow drain). It’s not a design flaw, nor an aesthetic choice—it’s a carefully engineered safety feature built into many sinks.
The Surprising Function: Preventing Overflow
The main purpose of the overflow hole is simple but crucial:
👉 It prevents water from spilling over the edge of the sink.
If you leave the tap running while the drain is blocked or closed, water will rise. Instead of flooding your bathroom counter or floor, excess water enters the overflow hole and is redirected safely into the drainpipe system.
How Does the Overflow Hole Work?
Behind the sink, there’s a hidden channel connecting:
- the overflow hole
- the main drain pipe
When water reaches the level of the overflow hole:
- It flows into the opening
- Travels through the internal channel
- Drains away safely
This system can prevent serious water damage caused by accidental overflows.
A Secondary Benefit: Improved Drainage Speed
Another lesser-known benefit is that the overflow hole:
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