Many folks might think that a sink overflow is when a sink overflows, but it is actually what prevents a sink from overflowing, which is sort of the opposite of what folks intuitively may think. A bathroom sink overflow drain is the one most commonly found of all plumbing fixtures.
What is an Overflow & Why is a Sink Overflow Important? A 5-Point Answer
Many if not most sinks have overflows below what is known as the flood rim level for several reasons related to functionality, design, and safety. You might not notice it or realize the purpose until you leave a sink running and unattended that gets clogged.
- Preventing Overflow of Water: The primary function of an overflow is to prevent the sink from overflowing in case the drain gets clogged or someone forgets to turn off the faucet, walks away, and gets distracted. This simple sink feature provides an additional outlet for water to escape before reaching the rim of the sink (which is known as the flood rim level in plumbing terms). That may be why bathroom sinks and tubs have an overflow, whereas most kitchen sinks and laundry tubs do not.
- Health, Hygiene, and Property Damage Concerns: Overflows can help in maintaining hygiene and preventing health issues (such as mold and mildew) by preventing stagnant and wastewater water from accumulating and overflowing from inside the sink basin. The top level of stagnant water can contain the most fouled wastewater (grease, soap, dirt, etc.) and be a breeding ground for bacteria and unpleasant odors. If a sink does overflow that same stuff will be seeping into your floor, molding, sheetrock, and inside your sink vanity.
- Design and Aesthetics: Some sinks with overflows are carefully designed with overflows to maintain a sleek and continuous appearance without interrupting the overall design. This is particularly common in modern and minimalist sink designs.
- Regulatory Requirements: Building codes and regulations in certain regions may mandate the inclusion of overflows in sink designs for safety and hygiene reasons.
- Material, Construction, and Purpose of the Sink: The presence or absence of an overflow may also depend on the material, construction, or purpose of the sink or plumbing fixture. Porcelain and ceramic sinks are more likely to have overflows due to the ease of integrating them into the design, whereas solid surface or metal sinks may not have them as frequently. Additionally, kitchen sinks are deep and not prone to be left unattended, as say a bathroom sink or bathtub might.
Specialty and Designer Sinks
In contrast, sinks without overflows are usually designed for specific purposes or aesthetics. For example, vessel sinks, which sit on top of the counter, often lack overflows because of their unique design and installation method. In many cases, if you want to make your overflow look nicer you can purchase a basin sink overflow cover.
Additionally, some designer sinks may omit overflows as a deliberate aesthetic choice. However, the absence of an overflow in a sink means that there is a higher risk of overflow if the drain becomes blocked, or if the faucet is left running and unattended.
A Sink and Overflow “Fun Fact” Involving Drain Cleaning
If your sink does have an overflow outlet it can make drain cleaning when you have a clogged sink a bit more challenging. If you trying to clear the sink clog using pressure (such as a drain bladder or by using baking soda and vinegar) the overflow will not let pressure build up inside the drain lines. In the same way, the overflow allows drain water to enter, it also allows air or gas pressure to escape.
Whenever you are trying to clear a sink clog using air or gas pressure (baking soda and vinegar clear clogs by the gas they create when combined) you will need to plug the overflow inlet inside the sink. Usually, you can wet the corner of a towel and stick it in, or some other such method.
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