What is the difference between S trap and P-trap bathroom sink?

What is the difference between S trap and P-trap bathroom sink?

December 23, 2022

When we are talking about sink traps, the functionality and efficiency of the sink are crucial. Plumbing traps play a significant role in maintaining proper drainage and preventing sewer gases from entering our living spaces.

In the world of bathroom sinks, two common trap configurations are the S-trap and the P-trap. In this article, we will delve into the details and explore the differences between these two types of traps.

Anatomy of a Plumbing Trap

Before discussing the specifics of S-trap and P-trap bathroom sinks, let's familiarize ourselves with the basic anatomy of a plumbing trap. A trap is a curved or U-shaped pipe section installed beneath the sink to retain a small amount of water, forming a seal. This seal prevents foul odors and harmful sewer gases from permeating into the bathroom. The trap also acts as a barrier, preventing debris from clogging the main drainage system.

The trap consists of several essential components. The trap arm connects the sink drain to the trap, while the trap seal is the water barrier within the trap itself. Finally, the inlet and outlet connections enable the trap to be connected to the waste pipes and the sink drain.

What are S-Trap Bathroom Sinks?

S-trap bathroom sinks derive their name from their distinctive shape, resembling the letter "S." In this configuration, the trap arm extends downward from the sink drain and connects to a horizontally positioned trap. The S-trap is commonly found in older buildings and may still be used in some regions. However, it has become less prevalent in modern construction due to its inherent drawbacks.

The design and installation of an S-trap require careful consideration. Firstly, the shape and appearance of the trap arm and trap itself may affect the overall aesthetics of the sink. Secondly, the trap arm must be installed with proper clearance to avoid interference with other plumbing components or adjacent walls. Finally, the connection between the S-trap and waste pipes should be tightly sealed to prevent leaks and maintain proper drainage.

S-Trap Bathroom Sinks: Pros and Cons

S-trap bathroom sinks have both advantages and disadvantages. On the positive side, the simplicity of their design makes them relatively easy to install and maintain. Additionally, the horizontal configuration of the trap may allow for better access in certain installation scenarios.

However, S-trap sinks also come with some drawbacks. One significant disadvantage is that the water seal in an S-trap can be easily compromised if the water level drops too low, resulting in sewer gas leakage. Furthermore, S-trap installations may not comply with modern building codes in certain areas, making them unsuitable for new constructions or renovations.

What are P-Trap Bathroom Sinks?

Unlike the S-trap, P-trap bathroom sinks feature a trap configuration that resembles the letter "P." The trap arm extends downward from the sink drain and connects to a vertical trap, which then connects to the waste pipes. P-traps are widely used in modern plumbing systems due to their effectiveness and compliance with building codes.

The design and installation of P-trap bathroom sinks share some similarities with S-trap configurations. However, P-trap installations generally require more vertical clearance beneath the sink to accommodate the vertical section of the trap. It is essential to ensure adequate space between the trap and other components or structures.

P-Trap Bathroom Sinks: Pros and Cons

P-trap bathroom sinks offer several advantages. Their vertical design allows for a more secure water seal, minimizing the risk of sewer gas leakage. P-traps also provide improved compatibility with modern plumbing standards and building codes. Moreover, the vertical orientation of the trap can facilitate easier maintenance and cleaning of the sink.

However, there are a few drawbacks associated with P-trap bathroom sinks. The installation of a P-trap may require more vertical clearance compared to an S-trap, which could be a limitation in some space-constrained scenarios. Additionally, the complexity of the trap design may make installation slightly more challenging than an S-trap. However, these disadvantages are often outweighed by the benefits of using a P-trap.

Comparison between S-Trap and P-Trap Bathroom Sinks

To better understand the differences between S-trap and P-trap bathroom sinks, let's compare various aspects of these configurations:

●Design and Appearance

The S-trap features a horizontal trap, while the P-trap has a vertical trap. This fundamental difference in design significantly affects the overall appearance of the sink. S-trap sinks may have a more traditional or retro look, while P-trap sinks offer a sleeker and modern aesthetic.

●Installation Requirements and Challenges

While both trap configurations require careful installation, the P-trap may pose a slightly higher level of complexity due to its vertical orientation. It often necessitates more vertical clearance beneath the sink, which could be a constraint in tight spaces. S-traps, on the other hand, may be easier to install in certain scenarios.

●Maintenance and Cleaning Considerations

When it comes to maintenance and cleaning, P-trap sinks have an advantage. The vertical design of the trap allows for easier access and cleaning of debris that may accumulate within the trap. S-trap sinks may require more effort and care during cleaning, especially considering the horizontal orientation of the trap.

●Performance and Effectiveness

In terms of performance, P-trap sinks generally offer better efficiency and effectiveness. The vertical orientation of the trap ensures a more secure water seal, minimizing the risk of sewer gas leakage. S-trap sinks, on the other hand, may be prone to losing their water seal if the water level drops too low, resulting in unpleasant odors.

●Local Building Codes and Regulations

Another critical factor to consider is local building codes and regulations. While S-trap sinks may still be allowed in some areas, many building codes now mandate the use of P-traps due to their improved performance and compliance with standards. It is essential to consult local authorities or a professional plumber to ensure compliance with relevant regulations.

Choosing the Right Bathroom Sink Trap

When selecting a trap for your bathroom sink, several factors should be considered. Firstly, familiarize yourself with local plumbing codes and regulations to ensure compliance. Additionally, assess the available space and the specific requirements of your bathroom. If space is limited, a P-trap may present challenges, whereas an S-trap could be a suitable alternative. However, for optimal performance and compatibility, a P-trap is generally recommended.

Consulting with a professional plumber can provide valuable insights and guidance in choosing the right trap for your specific needs. They can assess the space, consider local regulations, and recommend the most appropriate trap configuration for your bathroom sink.


In summary, the difference between S-trap and P-trap bathroom sinks lies in their design, installation requirements, maintenance considerations, performance, and compliance with local building codes. While S-trap sinks may have a more traditional appearance and simpler installation, P-trap sinks offer improved efficiency, better compliance, and easier maintenance.