S Trap vs P Trap

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Are you feeling trapped by your plumbing knowledge? Do you ponder the difference between an s trap vs p trap? Then this guide is here to save the day. It aims to clarify the distinctions between an S trap and a P trap, including their functions and typical usage scenarios.

After going through this, you will understand plumbing traps better, which will help you choose the most suitable one for your needs.

What is a Trap?

CIENCIA Sink Trap Brass S Trap for Bathroom Sink Kitchen Sink Sewer Pipe Drain Tube S Trap Chrome, WT04

JEAPHA Stainless Steel P-Trap - 1 1/4 Inch Bathroom Basin Sink Waste Trap with Reducing Washer, Chrome Finish

In plumbing, a trap is a device that is designed to prevent sewer gases and unpleasant odors from entering the living space. It is a bend or curve in the drainpipe that holds water and creates a barrier against the gases that can come up from the sewer system. Typically, traps are found beneath plumbing fixtures such as sinks and bathtubs.

Importance of a Trap

Traps are crucial components of plumbing systems, preventing sewer gases and odors from entering living spaces and preventing clogs by catching debris. Different types of traps are used depending on the plumbing fixture and the building’s plumbing code.

S traps and P traps are the most common types. Regular maintenance and proper installation are necessary to prevent health hazards and plumbing issues.

What is S trap?

Kingston Brass ST14190 Vintage 1-1/4-Inch Brass S-Trap, 18 Gauge, Matte Black

An S trap is a plumbing fixture that connects a sink, shower, or bathtub to a drain pipe and is named after its “S” shape. The curved section of a pipe traps a small amount of water to block sewer gases from entering the fixture while still allowing proper water flow. As water passes through the drain, it forms a siphon that removes the water from the trap.


  • S traps are generally less expensive than P traps, making them a popular choice for budget-conscious homeowners.
  • These can be easily installed and are compatible with different types of plumbing fixtures.
  • S traps are suitable for use in areas where the drain pipe is located below the fixture, such as in a basement or crawlspace.


  • S traps are more prone to siphoning than P traps, which can result in the loss of the water barrier and the release of sewer gases into the home.
  • They are not suitable for use in areas where the drain pipe is located above the fixture, such as in a second-story bathroom.
  • S traps are not compliant with modern plumbing codes in many areas and may need to be replaced with P traps in order to pass a home inspection.

What Is P Trap?

GORDEE Bathroom Basin Sink Bottle P Trap, Brass U-Shape 1-1/4 inch Slip Inlet Drain, Lavatory Adjustable Height Sink Waste Drain P-Trap Kit, Pls Measure ur Sink Hole Size Before Order, Matte Black

A P trap is a U-shaped plumbing fixture installed under the sink or other plumbing fixtures to prevent sewer gases from flowing back into the house. It creates a water seal that blocks gases from coming up when water flows down the drain. Additionally, the water in the P trap is a barrier to prevent insects and rodents from entering the house.


  • The P trap is an effective way to prevent sewer gases from entering the house.
  • It is easy to install and requires minimal maintenance.
  • The P trap is relatively inexpensive compared to other plumbing fixtures.
  • It is a standard plumbing fixture that is used in most homes.


  • The P trap can become clogged with debris, which can cause water to back up into the sink or other plumbing fixtures.
  • The water in the P trap can evaporate over time, which can break the seal and allow sewer gases to enter the house.
  • The P trap can be difficult to access if it is located in a tight space

Also Read: How to Connect P-trap to Wall Drain

P-Trap VS S-Trap

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EASTMAN 35400, White Heavy-Duty S-Trap with Adapter, 1-1/2 inch

In plumbing, two types of traps are commonly used: the P-trap and the S-trap. Both of these traps have the same function of blocking sewer gases from entering the building, but they have different designs and uses.

The Shape

The main difference between P-traps and S-traps is their shape. P-traps resemble the letter “P” and have a horizontal inlet and outlet with a downward bend that creates a water seal. S-traps resemble the letter “S” and have a vertical inlet and outlet with a downward bend that creates a water seal.

The Use of Vent

A key difference between P-traps and S-traps is the use of a vent. P-traps are designed to be used with vent pipes, which allow air to enter the plumbing system and prevent suction that can empty the trap. S-traps, on the other hand, are not designed for use with vent pipes, making them more prone to losing their water seal and allowing sewer gases to enter the building.

The Volume of Water Used

Another difference between the two traps is the volume of water used. P-traps require more water to create a seal than S-traps. This means that P-traps may be more prone to clogging if they are not used frequently enough, as the water in the trap can evaporate and leave debris behind.


The size of the trap can also differ between the two types. P-traps are typically larger than S-traps because they require more water to create a seal. This means that P-traps can take up more space under sinks or other plumbing fixtures.

Plumbing Cord Standards

Plumbing code standards dictate when and where each type of trap can be used. P-traps are more commonly used in modern plumbing systems and S-traps in older systems. While both P-traps and S-traps prevent sewer gases from entering the building, they differ in design and usage. Understanding these differences can help homeowners and plumbers choose the right trap for their specific needs.

Frequently Asked Questions

What is the difference between an S-trap and a P-trap?

An S-trap is a type of trap that is shaped like an “S”. It is used to prevent sewer gases from entering your home. A P-trap, on the other hand, is shaped like a “P”. It is used to prevent sewer gases from entering your home as well. The main difference between the two is the shape.

Which one is better, an S-trap or a P-trap?

The choice between an S-trap and a P-trap depends on your specific situation, and neither is inherently better than the other. If you have a small space, opt for an S-trap, as it is shorter. But, if you have a larger space, go for a P-trap, as it is less susceptible to clogging.

Can I replace an S-trap with a P-trap?

Yes, you can replace an S-trap with a P-trap. However, you will need to make sure that you have enough space for the P-trap. You may also need to make other adjustments to your plumbing system to accommodate the P-trap.

How do I know if I have an S-trap or a P-trap?

The easiest way to tell if you have an S-trap or a P-trap is to look at the shape. If it is shaped like an “S”, then it is an S-trap, and if it is shaped like a “P”, then it is a P-trap.


To summarize, when selecting a plumbing system trap (S-trap or P-trap), it’s crucial to think about its design and function. Although S-traps are easier to install and require less area, they are more susceptible to siphoning and gas leaks.

On the contrary, P-traps are better at avoiding these problems, but they require more room and are harder to mount.

Additionally, it’s important to keep in mind that there are alternative traps accessible that suit your specific requirements. By comprehending the qualities of each type, you can make a well-informed choice. And select the finest trap for your plumbing system.

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