That Little Hole at the Top of Your Sink, Explained

Updated: Jan. 26, 2022

Have you ever wondered about that hole near the top of your bathroom sink?

sinkFrancesco Cantone/Shutterstock

Have you ever wondered about that hole near the top of your bathroom sink?

Hole In Sink: Explained

Depending on the design of your sink, it may have one, two or three holes, and they may appear between the faucet valves, facing toward you, or under the near rim, facing the mirror. They serve two functions: to prevent an overflow with the drain stopper engaged and to provide an escape route for air in the drain. Without this hole, a full basin of water would drain slowly because of the resistance it puts on air escaping up from the drain. An alternate escape route keeps air moving and the drain line flowing at full capacity.

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You may have noticed that your bathtub has an overflow vent hole, too, but not your kitchen sink. 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.

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Another concern that prevents an overflow hole from appearing in the kitchen sink: bacteria. That little passage can harbor bacteria that may contaminate food or even dishes and utensils as you clean them, with the potential to make you sick.

Occasionally, bacterial growth in the sink overflow vent causes a foul odor. This signal is your alert that cleaning is past due.

Clean the hole in your sink with a four-step process:

  1. Start by loosening anything attached to the sides of the passage from the overflow/vent opening to the drain line. An inexpensive pipe-cleaner-type brush makes the job simple.
  2. Boil several cups of water, insert the tip of a funnel into the hole and flush out the tube.
  3. Treat the tube with an enzymatic drain cleaner (septic-safe options available) and let it sit overnight, or flush with 2 cups of a 1:1 solution of baking soda and vinegar and let it sit for 15 minutes.
  4. Complete the job by flushing a final time with several cups of boiling water.

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