What's the Difference between P-Traps and S-Traps? 

P-Traps and S-Traps: What’s the Difference? 

When it comes to home plumbing, the P-traps and S-traps are two fundamental components that are often mentioned. Understanding the differences between P-traps and S-traps can help homeowners make informed decisions about their plumbing systems, whether they are dealing with new installations, repairs, or remodels.

Understanding Plumbing Traps

Before diving into the specifics of P-traps and S-traps, it’s useful to first understand the purpose of a trap in plumbing, and why they are essential.

What is a Plumbing Trap?

A plumbing trap is a curved section of a drainpipe that is designed to hold a small amount of water at all times. This water forms a seal that prevents sewer gases from escaping into your home. Traps are an essential part of any plumbing system because they protect your household from potentially harmful fumes while allowing wastewater to flow smoothly through the pipes.

The P-Trap

The P-Trap

Design and Structure

The P-trap is named after its “P” shape when viewed from the side. It consists of a curved section of pipe that connects to the drain and a horizontal section that connects to the wall or floor drain line.

How It Works

The P-trap holds water in its curve, creating a barrier that blocks sewer gases from backing up into the house. When water flows through the drain, it pushes the existing water out of the trap and replaces it with new water, maintaining the seal.


  • Effective at Preventing Sewer Gas: The P-trap effectively keeps sewer gases at bay, ensuring a safe and odor-free environment.
  • Easy to Clean: The design makes it relatively easy to remove clogs and debris by disassembling the trap.
  • Widely Accepted: P-traps meet most modern plumbing codes and are commonly used in residential and commercial plumbing systems.


  • Space Requirement: P-traps require more horizontal space, which might be a limitation in tight installations.

The S-Trap

The S-Trap

Design and Structure

The S-trap gets its name from its “S” shape. It features a similar curved design to the P-trap but connects to the plumbing system in a different manner. The S-trap has two curves and typically goes directly into the floor rather than connecting horizontally to a wall drain.

How It Works

Like the P-trap, the S-trap holds water to block sewer gases. However, its design can sometimes cause problems with siphoning, where the water seal is lost due to excessive water flow creating a vacuum effect.


  • Compact Design: S-traps can be more compact and easier to install in tight spaces where P-traps may not fit.
  • Older Homes: They are commonly found in older homes and may be grandfathered in under older plumbing codes.


  • Prone to Siphoning: S-traps are more likely to lose their water seal due to siphoning, which can allow sewer gases to escape.
  • Not Code-Compliant in Many Areas: Many modern plumbing codes do not allow S-traps for new installations because of their siphoning issues.

P-Traps and S-Traps: Which One Should You Choose?

As a homeowner, deciding between a P-traps and an S-traps comes down to code compliance, reliability, and space considerations. Here’s a quick guide to help you make an informed choice:

When to Choose a P-Trap

  • New Installations: If you’re installing new plumbing, P-traps are generally the preferred choice due to their code compliance and effectiveness.
  • Remodels: When renovating your bathroom or kitchen, upgrading to a P-trap can provide better long-term reliability.
  • Reliability: If avoiding sewer gas issues is a top priority, the P-trap’s design offers greater assurance against siphoning.

When to Consider an S-Trap

  • Older Homes: If you live in an older home with existing S-traps, replacing them might not be immediately necessary unless you encounter problems.
  • Space Constraints: In rare cases where space is extremely limited, and no other options are available, an S-trap might be the only feasible solution, although consulting with a professional plumber is recommended.

Maintenance and Repairs

Regardless of whether you have a P-trap or an S-trap, regular maintenance and timely repairs are crucial to keeping your plumbing system functioning correctly. Here are some tips from professional plumbing services for maintaining your traps:

  • Check for Leaks: Inspect the trap regularly for any leaks or signs of corrosion that could compromise its effectiveness.
  • Repair if Needed:  If you notice any issues with your trap, such as a broken seal or damaged pipe, have it repaired promptly by a professional plumber.
  • Replace When Necessary: If you encounter persistent problems with your trap, it may be time to replace it entirely.

Other Types of Plumbing Traps

P-Traps and S-Traps and other Types of Plumbing Traps

While P-Traps and S-Traps are the most common types of plumbing traps, there are several others:

Bottle Trap

The bottle trap is distinct in its design, which resembles the shape of a bottle. It is frequently used in places where space below the sink is limited, such as in bathrooms and under kitchen sinks. The primary benefit of the bottle trap is its compact nature, making it ideal for minimalist installations. It also offers easy access for cleaning, as the bottom can usually be unscrewed to remove debris.

Drum Trap

The drum trap is another type of plumbing trap, often found in older homes. Named for its drum-like shape, this trap is larger than other types and effectively prevents sewer gases from entering the home. However, its larger size tends to collect more debris, which can make it more prone to clogs. Drum traps are less common in modern plumbing systems due to these maintenance challenges.

Bell Trap

Bell traps are commonly used in floor drains, particularly in garages and basements. The trap consists of an inverted bell-shaped cover that fits over a water-filled base. This design allows water to drain effectively while preventing gases from escaping. However, bell traps are not typically recommended for indoor use because their water seals are more prone to drying out, which could lead to gas leaks.

Inline Trap

The inline trap, as the name suggests, is incorporated directly into the drain line. It is primarily used in equipment and appliances where space is a concern and is often seen in commercial kitchen applications. These traps are efficient and convenient when placed in hard-to-access areas, although they may require specialized cleaning equipment to maintain.

Grease Trap

Grease traps, also known as grease interceptors, are essential in commercial kitchens and food service operations. They are designed to capture and separate fats, oils, and grease (FOG) from wastewater before it enters the municipal sewer system. Grease traps come in various sizes and configurations, and their maintenance involves regular cleaning to prevent blockages and ensure efficient operation.

HepvO Waterless Trap

The HepvO waterless trap is a modern innovation that uses a self-sealing membrane instead of water to block sewer gases. This trap is designed to prevent evaporation issues associated with traditional water-filled traps. It is an ideal solution for infrequently used drains, such as those in vacation homes or seasonal properties, providing a reliable and maintenance-free alternative.


Both P-traps and S-traps have their uses and benefits, but understanding their differences is crucial for maintaining a safe and efficient plumbing system. For most modern applications, the P-trap is the superior choice due to its reliability and compliance with current plumbing standards.

If you’re considering a plumbing project or upgrade, always consult with a professional plumber to ensure your system is up to code and meets your household needs.

Your Florida Plumbing Experts

Whether it’s septic tank services or plumbing services you need, call the best plumbing company – Stronghold Plumbing & Septic.

We are the Lakeland plumber that’s there when you need us, 24/7. Reach out today and ask about our free plumbing estimates.

FAQ’s – P Traps and S Traps

What is the purpose of a P-trap or S-trap?

The main purpose of both traps is to prevent sewer gases from escaping into your home by holding water in their curved sections.

Which trap is more common in modern plumbing systems?

P-traps are generally more commonly used in modern plumbing systems due to their effectiveness and compliance with current codes.

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

Yes, it’s recommended to replace an S-trap with a P-trap for better reliability and code compliance.

Do all plumbing systems require traps?

Yes, all plumbing systems should have some form of trap to prevent sewer gas buildup and protect against clogs.


Leave a Reply

Your email address will not be published. Required fields are marked *

Similar Stories

A plumber using a wrench to fix a noisy faucet.

How to Fix a Noisy Faucet: A Step-by-Step Guide

Whether in the bathroom, kitchen, laundry room, or even outside, a noisy faucet can be more than just a minor annoyance; it can also be ...
Read More →
Difference Between Hard Water and Soft Water?

Hard Water vs. Soft Water: Understanding the Key Differences

Most people know that the makeup of water is H₂O, but this disguises the fact that not all water is created equal. Minerals in water ...
Read More →

Single-Flush vs. Dual-Flush Toilets

When it comes to renovating your bathroom or making eco-friendly choices for your home, the type of toilet you install plays a crucial role. With ...
Read More →
A plumber using a wrench to fix a noisy faucet.

How to Fix a Noisy Faucet: A Step-by-Step Guide

Whether in the bathroom, kitchen, laundry room, or even outside, a noisy faucet can be more than just a minor annoyance; it can also be ...
Read More →
Difference Between Hard Water and Soft Water?

Hard Water vs. Soft Water: Understanding the Key Differences

Most people know that the makeup of water is H₂O, but this disguises the fact that not all water is created equal. Minerals in water ...
Read More →
Stronghold Plumbing Badge

Get Affordable Septic Services in Lakeland Now!

We’re standing by and ready to respond.