Nothing could be more frustrating than dealing with a double kitchen sink that keeps backing up. It can transform a functional kitchen into a chaotic mess in no time. This blog will answer the question many homeowners ask: “Why is my kitchen sink backing up?” Understanding the causes of a clogged sink can help you tackle the problem quickly, save money on repairs, and keep your kitchen clean and hassle-free.

Double Kitchen Sink

Clogged P-Trap

The ‘P-Trap’ is the curved pipe located underneath your sink, named for its shape like a sideways “P.” This trap’s purpose is to prevent sewer gasses from rising into your home, but it can often become a catch-all for debris and waste.


Every time you rinse food particles or grease down the sink, there’s a chance that some of it may get stuck in the P-trap. Over time, these particles can accumulate, causing a slow drain or even a complete blockage. In double sinks, a common problem is when the kitchen sink backs up into the other side. If one side is clogged, water can appear to back up into the other side.


Blocked Vent

In addition to the P-Trap, your kitchen double sink plumbing system includes vents that allow sewer gasses to escape and air to enter, maintaining the pressure balance. It can disrupt this balance if leaves, bird nests, or snow block the vent. The lack of air can create a vacuum in the system, leading to slow drainage or backups.


Shared Pipe Blockage

A double kitchen sink usually shares a common drain pipe. If the blockage occurs in the shared drain pipe, both sides of your double sink can back up simultaneously. Common culprits for this blockage include grease, large food particles, or non-food items accidentally dropped down the drain.


Faulty Garbage Disposal

If your double kitchen sink features garbage disposal on one side, then issues with this apparatus could be the root of your troubles. This common household tool is fantastic for grinding food waste and ensuring it passes through your plumbing system smoothly. However, when things go awry with your garbage disposal, it can lead to a kitchen sink backup.


It could be a matter of the disposal being clogged with food debris, especially from materials it struggles to process. Examples include fibrous vegetables, bones, or overly starchy foods, which create a paste-like substance that sticks to the pipes. The problem could also arise if your disposal isn’t used often enough, causing food debris to sit and potentially harden or rot.


Plumbing Issues Beyond the Sink

Sometimes the issue is bigger than your sink. If your home’s main sewer line becomes clogged, water can back up into the lower drains, including your kitchen sink. Tree roots, accumulated waste, or even collapsed pipes can cause a main sewer line blockage.


Proactive Measures: Tips to Avoid Double Kitchen Sink Backing Up

Preventing sink backups is more desirable than dealing with the fallout. Here are some proactive measures to keep your double kitchen sink functioning optimally:


Avoid Dumping Grease: Grease may go down the drain as a liquid but will cool and solidify within your pipes, creating a sticky trap for other debris and leading to clogs. Instead, pour grease into a heat-resistant container, let it solidify, and dispose of it in the trash.


Limit Food Waste in Disposal: Your garbage disposal isn’t a substitute for your trash can. Avoid putting fibrous or starchy foods, bones, and coffee grounds at your garbage disposal. These can bind together, creating stubborn clogs.


Use Sink Strainers: A sink strainer can capture large particles that might otherwise find their way into your pipes. Just remember to clean the filter regularly.


Regular Cleaning: Routinely clean your sink and disposal with hot water and dish soap or a DIY vinegar and baking soda concoction, which can help break down buildup and keep your drains clear.


Professional Maintenance: Schedule regular maintenance checks with a professional plumbing service. These experts can spot and resolve minor issues before they become major problems.



A kitchen sink backup is more than just a nuisance; it’s a clear sign that something is not quite right in your plumbing system. However, by identifying the potential causes, you can take steps towards resolving the problem.


If the issue is localized, like a clogged P-trap or garbage disposal, it may be something you can fix yourself. On the other hand, more extensive issues like blocked vents or sewer line blockages may require a professional plumber’s attention.


Remember, prevention is better than cure. Regular maintenance, mindful usage of your sink, avoiding pouring grease or large particles down the drain, and running your garbage disposal properly can help avoid many of these issues in the future. By staying on top of potential problems, you can keep your kitchen plumbing in check and your double sink flowing smoothly.


What’s Next?

Plumbing issues can get out of hand, no matter how well-prepared you are. If you are dealing with a backed-up double sink that you can’t fix on your own, don’t stress – the professionals at New Flow Plumbing are ready to assist.


Our team of licensed plumbers has the skills, knowledge, and equipment to handle all your plumbing problems, no matter how complex. We’ll not only help fix the current issue but also provide advice and solutions to prevent future backups. Contact us today, and let us restore the flow to your double kitchen sink!

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