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How does my kitchen sink drain to the sewer?

14–16 minutes to read

In a typical residential setting, your kitchen sink drains to the sewer through a system of pipes connected to your home’s plumbing network. Here’s a general overview of each part that creates the network, and how it works.

Sink Drain

The kitchen sink has a drain located at the bottom, typically covered by a strainer or plug. When you remove the strainer or open the plug, water and waste can flow into the drain.


Directly beneath the sink, there is a U-shaped pipe called a trap. The trap is designed to hold water, which forms a seal that prevents sewer gases from entering your home. It also helps trap small objects that might accidentally fall into the sink, preventing them from entering the main plumbing system.


Below the trap, there is a vertical pipe known as the drainpipe. This pipe extends downward and connects to the sewer line or the main plumbing system of your home.

Sewer Line

The drainpipe from your kitchen sink connects to the larger sewer line or wastewater plumbing system of your house. The sewer line carries all the wastewater from your home, including that from your kitchen sink, toilets, showers, and other drains, to the municipal sewer system or your private septic tank.

Sewer System/Septic Tank

Depending on your location, your home’s wastewater may be directed to a municipal sewer system or a septic tank. In a municipal system, the wastewater flows through a series of underground pipes that transport it to a sewage treatment plant. In a septic system, the wastewater enters a septic tank on your property, where it undergoes natural bacterial decomposition before being dispersed into a drain field.

It’s important to note that plumbing systems can vary, and the specific layout of your kitchen sink drain may depend on your house’s design and local building codes. Consulting a plumber or referring to the blueprints of your home can provide you with more accurate information about your kitchen sink’s drainage system.

Kitchen Drain Design

A kitchen sink incorporates several components to prevent sewer smells and keep the drainage system clear.

It’s worth noting that waste disposals are not designed to handle all types of waste, and certain items like large bones, fibrous foods (e.g., corn husks), grease, and non-food items should not be disposed of in them. Proper usage and regular maintenance are important to prevent clogs and maintain the functionality of a waste disposal unit.

The strainer is a removable device placed over the drain opening to catch solid waste such as food particles, debris, or utensils that may accidentally fall into the sink. It helps prevent these objects from entering the plumbing system, which could potentially cause clogs or damage. If you are experiencing issues with your water slowly draining away, this may be due to a damaged seal or more commonly, incorrect installation. For more information on this, please see our blog ‘Why your kitchen sink may not be holding water‘.

As mentioned earlier, the trap is a U-shaped pipe located below the sink. It holds a small amount of water in its bend, forming a water seal or barrier. This seal prevents foul odours and sewer gases from traveling back up through the drain and into your home. The water in the trap effectively blocks the gases from the sewer line while still allowing water and waste to flow through.

Waste Disposal Unit

A waste disposal unit is an optional device installed beneath the kitchen sink. It helps break down food waste into smaller particles that can be flushed away through the plumbing system. Waste disposals typically consist of a motorized grinding mechanism that shreds the waste and allows it to be easily washed away. While they can be convenient for disposing of food waste, they are not a necessity in every kitchen and depend on personal preference.

The combination of a strainer, trap, and optional waste disposal unit helps prevent sewer smells by trapping solid waste, creating a water seal to block odours, and providing a mechanism to break down food waste. Regular cleaning, proper waste disposal practices, and occasional maintenance can help keep the kitchen sink drainage system clear and functioning effectively.

To shop our waste and plumbing kits, please click here.

What causes a kitchen sink to smell?

A kitchen sink can develop unpleasant odours due to various factors. There are some common causes of kitchen sink smells found quite commonly in homes.

Food Waste: Food particles that accumulate in the drain or garbage disposal can decompose over time, producing foul odours.

Grease and Fat Buildup: Grease, oils, and fats that are poured down the drain can solidify and accumulate in the pipes, leading to odor-causing bacteria growth.

Clogs: Partial clogs or blockages in the drain can cause stagnant water to accumulate, which can emit unpleasant smells.

Failing Trap Seal: The trap beneath the sink holds a small amount of water that forms a seal, preventing sewer gases from entering your home. If the water in the trap evaporates, the seal breaks, allowing odours to escape

Now, let’s discuss how a trap works and how to fix a failed trap seal.

A trap is a U-shaped pipe located beneath the sink. It is designed to hold water in its bend, creating a water seal. This seal prevents sewer gases from traveling back up through the drain and into your home.

If the water in the trap evaporates over time, such as when a sink is infrequently used, the trap seal can fail, resulting in odours.

How do I stop my kitchen sink smelling?

Check the Trap. Locate the trap beneath your sink and visually inspect it. Ensure there are no leaks, cracks, or other damage that may be causing the water to drain out.

Pour Water down the sink. If the trap appears intact, pour water directly into the drain to refill the trap. This replenishes the water seal and blocks the entry of sewer gases. Use enough water to fill the trap completely.

Run Water Regularly. To prevent the trap seal from drying out in the future, run water through the sink regularly, even if you’re not using it for extended periods. This helps maintain the water level in the trap and prevents evaporation.

If you continue to experience trap seal failures or persistent odours despite following these steps, it may be advisable to consult a plumber. They can inspect your plumbing system and address any underlying issues that may be contributing to the problem.

Additionally, practicing good waste disposal habits, such as avoiding pouring grease down the drain and using a strainer to catch food particles, can help prevent odour issues in the kitchen sink.

Waste disposals

Waste disposals are devices installed beneath the kitchen sink to help dispose of food waste. Here’s an overview of how they work and how to maintain them:

Operation: Waste disposals consist of a motorized grinding mechanism and a shredding plate or impeller. When you turn on the disposal unit, typically by flipping a switch on the wall or activating a button on the unit itself, the motor starts rotating the grinding mechanism.

Grinding: As the motor spins the grinding mechanism, food waste that is fed into the disposal unit is chopped into small particles. The sharp blades or impellers break down the waste, reducing it to a size that can easily flow through the plumbing system.

Flushing: Once the waste is ground up, water from the sink is used to flush the particles through the plumbing system. The running water helps wash away the ground waste, preventing it from accumulating in the unit or the pipes.

Maintenance tips for waste your disposal:

  • Proper Use: Only dispose of suitable food waste in the waste disposal. Avoid putting non-food items, large bones, fibrous materials e.g. coffee grounds, and grease or fat down the disposal. These can clog the unit or impede its functioning.
  • Cold Water: Run cold water before, during, and after using the waste disposal. Cold water helps solidify any fats or oils present, making it easier for the unit to grind and flush them away.
  • Regular Cleaning: Periodically clean the disposal to remove build-up and odours. You can use a combination of ice cubes and rock salt by putting them in the disposal and running it for a few seconds. This helps dislodge debris and provides a mild abrasive action. Alternatively, you can use specialized disposal cleaning products.
  • Citrus or Vinegar: To combat odours, you can cut a citrus fruit (such as a lemon or lime) into small pieces, run them through the disposal, and flush with cold water. Alternatively, you can pour vinegar into the disposal and let it sit for a few minutes before flushing it with water.
  • Professional Maintenance: If you notice persistent issues or unusual noises coming from the disposal, it’s advisable to contact a professional plumber or service technician. They can inspect and service the unit as needed.

For more information on how waste disposals work, please see our blog, What is a kitchen waste disposal? Alternatively, to shop our waste disposal units, click here.

A way to help keep your plumbing system fresh is to use cleaning products such as the Glisten Waste Disposal Cleaning Sachets periodically. This will help to eliminate odours and prevent build-up.

Remember to always follow the manufacturer’s instructions for your specific waste disposal unit, as different models may have varying maintenance requirements.

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