The small hole located near the top of your bathroom sink is called the overflow. The overflow allows for ventilation and captures excess water before the sink spills over. Some sinks have more than one overflow hole, located opposite or under the faucet. Like any area in your home, it needs a good cleaning every once in a while. Since it works both as a vent and to protect against a flooded sink, it's important to keep it clean and clear.
Tools of the Trade
When there is visible buildup or general grossness growing in the overflow, a professional but inexpensive tool can be used to push through the gunk.
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Drain and sink overflow cleaning brushes are another name for pipe cleaners. The long, wiry brush or pipe cleaner can fit into the overflow hole and remove some of the physical buildup by pushing it in and out several times to reach the drain walls.
A funnel is the next tool you'll use. Remove the pipe cleaner and insert the funnel into the overflow hole. Boil about 2 quarts of water and pour into the overflow hole to flush out the rest of the buildup.
Bacteria growing in the overflow drain can cause an unpleasant odor. Simply cleaning with boiling water will not get rid of the smell because it may not kill the bacteria. Enzyme cleaners are made to "eat" the organic bacteria and clean out the cause of the stench. Enzyme drain cleaners are sold at home improvement stores, and some will note if they are safe for drains that flow into septic tanks. Some enzyme cleaners come in powder form and must be mixed. Others are in liquid form and ready to go. Use a funnel to pour the enzyme mix down the overflow hole. Let it sit overnight to work on the bacteria, and flush with warm water the next day.
Baking Soda and Vinegar
A deep cleaning of your overflow drain can be done with baking soda and vinegar. These two ingredients mix together to create a foaming, cleaning, deodorizing solution that cleans the area without using harsh chemicals. Insert a funnel in the overflow hole and carefully pour 1 cup of baking soda into the funnel. Slowly add 1 cup of white vinegar on top of the baking soda. The mix will foam up and move down the drain. Leave the mix in the overflow hole for around 10 minutes, and follow up with boiling water to flush out cleaner and help sanitize the overflow drain.