Cleaning Tips, Guides & Resources

The Purpose and Maintenance of a Sink Overflow

the purpose and maintenance of a sink overflow custom graphic

If you’re one of the surprisingly many people who are unaware of what a ‘sink overflow’ is, that’s about to change! While they are not exclusively featured in sinks, and can be found on other fixtures like bathtubs, an “overflow” is literally an extra drain for the sake of managing the possible overflow of water. They are identified as the small hole(s) along the upper edge of the sink. This particular drain can be found either under the faucet itself, or directly opposite the faucet along the inner wall of the sink. 

Although the overflow and regular sink drain are separate, they merge into the same drain pipe underneath the sink. While you could possibly see this under your sink (depending on what sink you have), most modern-day sinks have overflow drains inside the body of the sink itself, making it invisible. The only real difference here is that the overflow drain cannot be sealed like the regular drain with a stopper.

What is the Purpose of an Overflow Drain?

There are two main reasons why a sink should have an overflow drain. Let’s learn a little more about them below.

1) Preventing Overflow

This is a no-brainer; the idea of the overflow drain is, in fact, to handle overflow of water from the sink or tub in question. It is designed so that in the event that the regular drain on the sink has a stopper in place, and the faucet is left running, the water will not overflow from the sink, and spill over onto the floor. 

With that said, overflow drain holes are usually fairly small; this means there’s a possibility that they may not prevent an overflow of water entirely, but just delay it long enough for someone to know there’s an open faucet that needs to be closed.

2) Better Drainage

Beyond the name, the overflow drain being connected to the main sink drain itself means that it will allow air into the pipes from above. When water completely envelops the regular sink drain, a vacuum can occur and prevent the water from draining out quickly enough. The access to air from the overflow drain means that the water will not be slowed down, and will flow into the drain easily. If you see bubbles coming out of the drain when there’s a lot of water draining, then your sink probably doesn't have any kind of overflow opening to prevent this from happening.

How to Clean a Sink Overflow Drain

Since a sink overflow is a drain, ensuring it is clean and free from any kind of dirt or debris on the inside is important. Given enough time, dirt can build up in the pipes causing a blockage in the drain system.

The best way around this is to manually clean the overflow drain every now and then, and we are going to explain a few different ways to go about this. Take a look below.

1) Unclogging or Flushing

There are a few good options when it comes to unclogging or flushing overflow drains, and they are all quite simple.

Pipe Cleaner Brush

If you happen to have a pipe-cleaner brush that can fit into the overflow drain, then this will work really well. Simply work the brush into the drain, and slide it in and out a few times to really scrub the dirt loose. The key here is to do this slowly and carefully to prevent spraying any of the dirt out of the drain and into the sink. After a while of scrubbing, it’s best to flush the drain with some hot water. Do this with a heat-resistant funnel, and consider wearing silicone kitchen gloves to prevent accidentally burning yourself. 

Rubber Hose

Beyond this, another easy way to unclog the overflow sink drain would be to use any rubber hose that you can put against the overflow drain, and blow through it. Simply fill the sink up with water just a little higher than the overflow drain, and place one end of the hose against it. Using the other end, blow air into the hose a few times to force any dirt loose. After this, drain the sink normally and blow through the overflow with the hose again to ensure this has worked. This time around, you should feel far less pressure as you blow air into the drain.

Liquid Drain Cleaner

If you happen to have a bleach-based drain cleaner, make a solution with it using one part water, one part cleaner. This solution must be poured into the overflow drain via a funnel or container with a spout, and must sit there for 10 minutes. Once it has had time to settle, continue to rinse and flush the overflow with clean water until you are satisfied with the result. 

2) Cleaning Mould Buildup

If unclogging the drain isn’t the problem but there is a bad smell coming from your sink, you could be dealing with mould. In this case, a good cleaning is definitely in order.

Fortunately, there is a simple way to kill mould in your sink overflow, but for this process, we’ll need a few things to do it right. These include the following:

  • Baking Soda
  • Distilled White Vinegar
  • Boiling Water
  • Heat-resistant Funnel

Instructions: Take the funnel, place it into the sink overflow drain, and pour about a cup-full of baking soda into the drain. Immediately after this, pour one cup of white vinegar down the funnel. Once the two react, the solution will begin breaking down and dislodging any gunk stuck inside the drain. Allow this to rest for about 15 minutes before you flush the drain with boiling water. You may repeat this process if necessary, until the mouldy smell has gone completely. 


Ensuring your sink overflow drain is clean is important for better drainage, and to be prepared in the event that a faucet is accidentally left running. The key thing to keep in mind here is to clean the overflow and regular sink drain routinely to prevent them from turning into a problem where professional assistance is needed. For the most part, however, as long as you follow the guide above, you shouldn’t have a problem handling a small clog in a sink overflow. If your sink has overflowed and you need a deep clean, please don't hesitate to get in touch with us. 

Adriana Aziz is the operations manager at MaidForYou. With over 6 years of experience managing cleaning operations, she knows all the best hacks when it comes to cleaning residential and commercial buildings. With expert experience in managing house cleaning operations, interior design and logistics. She spends her free time with her family and as a freelance food critic.

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