When building or renovating a house in Kenya, plumbing might not be the first thing on your mind — but it's one of the most important. A well-designed drainage system keeps your home free from unpleasant smells and harmful sewer gases.
Two of the most common plumbing components that make this possible are the P trap and the S trap.
Although both serve the same purpose — to block foul odours from escaping through the drainage — their design, functionality, and ideal use cases differ. Understanding these differences helps homeowners and plumbers make better, safer, and more cost-effective decisions.
🏠 What Is a P Trap?
A P trap is a plumbing fixture named after its distinctive P-shaped curve when viewed from the side.
It consists of a U-shaped bend followed by a horizontal pipe that connects to the wall drainage system. The trap holds a small amount of water, creating a seal that prevents sewer gases from entering indoor spaces.
Every time you use your sink, shower, or washing machine, some water remains trapped in the curve. This small pool of water forms a protective barrier against odours and harmful gases.
Because of its reliability and compliance with modern building codes, the P trap is now the standard choice in most Kenyan homes and buildings.
🔧 Where Is a P Trap Commonly Used?
P traps are installed in fixtures that drain through the wall rather than the floor. They are suitable for most modern plumbing systems, especially those with venting provisions.
Common uses include:
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Bathroom sinks – to block odours and maintain hygiene.
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Kitchen sinks – to stop food smells and grease buildup.
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Bathtubs and showers – to ensure smooth drainage while sealing off gases.
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Washing machines – to control wastewater flow and prevent backflow odours.
⚙️ How Does a P Trap Work?
Each time you run water, part of it stays in the curved section of the trap. This forms a water seal that blocks gases from rising back into the room.
To function properly, the P trap must be vented — a vent pipe allows air to balance pressure, preventing siphoning (when fast drainage pulls the water seal out of the trap).
This simple yet clever design ensures that your drainage remains odour-free and efficient.
🚽 What Is an S Trap?
An S trap is an older type of plumbing trap shaped like the letter S. It curves downward and then back up before connecting vertically into the floor drain.
S traps were common in older homes and buildings where pipes drained directly into the floor — before venting systems became standard.
Just like the P trap, the S trap holds water to block sewer gases. However, it lacks proper venting, which can cause serious problems.
⚠️ Why S Traps Are Less Common Today
The biggest issue with S traps is siphoning. When water drains quickly, it can create a vacuum that pulls the seal water out of the trap.
Once the seal is gone, odours and gases escape freely into your home. Because of this, S traps are now banned in many plumbing codes around the world, including those applied by modern Kenyan building standards.
They are mostly found in older buildings or rural setups with outdated plumbing.
💡 P Trap vs S Trap: Key Differences
| Feature | P Trap | S Trap |
| Shape | P-shaped, connects to wall | S-shaped, connects to floor |
| Venting | Has a vent pipe | Lacks venting |
| Siphoning risk | Very low | High |
| Odour control | Reliable | Unreliable |
| Compliance | Meets modern codes | Outdated and often prohibited |
✅ Why P Traps Are the Better Choice
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Prevents Odours Effectively
The water seal and venting system ensure gases can't escape, keeping your home fresh.
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Complies with Modern Plumbing Codes
Building standards in Kenya favour vented systems — meaning P traps are fully compliant.
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Reduced Risk of Siphoning
The vent maintains pressure, keeping the water seal intact even during heavy drainage.
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Long-Term Reliability
P traps are durable, easy to maintain, and ideal for modern homes and apartments.
🏗️ Conclusion
When comparing P traps vs S traps, both play the same fundamental role — preventing sewer gases from entering your home.
However, P traps are clearly superior for modern plumbing systems. They're vented, safe, efficient, and compliant with current building standards.
If you're building or renovating your home in Kenya, always insist that your plumber installs a P trap system — especially for sinks, showers, and washing machines.
It's a small investment that guarantees better hygiene, long-term functionality, and peace of mind.
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