Post By Admin
February 6, 2026When renovating a bathroom or replacing an old toilet, many people focus on style, size, or flushing system, but often overlook one of the most critical details: the trap type.
Choosing between a toilet P-trap and an S-trap is not only about appearance, but also about how your toilet connects to the home’s plumbing system. Getting it wrong can lead to costly mistakes, awkward fittings, or inefficient performance.
A toilet trap is the curved section of the pipe that creates a water seal, blocking sewer gases from entering the bathroom. Every toilet has a trap, but the way it connects differs depending on whether it is a P-trap or an S-trap.
If you have noticed foul odours, leaks, or blockages, arranging a toilet repair service is often the best starting point. But understanding your trap type is just as important when planning upgrades.
Key Takeaways
- P-Trap and S-Trap work in the same way by holding water in the bend to block sewer gases, but they are not interchangeable without plumbing changes.
- When the waste outlet runs into the wall, the toilet uses a P-trap. This setup is common in modern Australian homes as it creates a cleaner look with minimal visible pipework.
- But if the waste outlet goes straight into the floor, then the toilet uses an S-trap. This design is typically found in older homes and is often the easiest option when replacing an existing toilet.
- Before upgrading or replacing a toilet, checking your existing trap type and toilet set-out can help prevent installation issues, extra costs, or the need for unnecessary plumbing work.
What is a P-Trap Toilet?
A toilet P-trap is designed so the outlet pipe connects horizontally into the wall rather than the floor. The curved shape resembles the letter P before it leads into the wall pipe.
This type of toilet is commonly found in modern Australian homes, as it suits bathrooms with wall plumbing connections.
Many new builds feature a P-trap under toilet installation, because it produces a clean finish and leaves less exposed piping.
Many people often prefer this system for its tidy look because it is easier to combine with modern feature. For example, an updated toilet flushing mechanism or a high-performance power flush toilet.
How Does a P-Trap Toilet Work?
A toilet P-trap works by keeping a small amount of water inside the bend after every flush. This water forms a barrier that stops sewer gases from escaping into the bathroom.
When flushed, waste flows past the water seal, through the horizontal outlet, and into the wall drainage system.
This design is highly effective in homes with wall outlets. However, if the trap becomes blocked, the toilet may stop flushing as it should.
When you experience issues such as your toilet not flushing properly, the cause may be a buildup inside the trap that needs to be cleared either manually or by a plumber.
Pros and Cons of Installing a P-Trap Toilet
When weighing up the option of installing a P-trap toilet, it is helpful to understand the strengths and weaknesses of this design. While it offers a modern and tidy solution, it does not suit every type of bathroom layout.
Advantages:
Before looking at the drawbacks, consider why a P-trap toilet is becoming the standard choice in modern homes.
- A P-trap toilet works perfectly with wall plumbing outlets. The straight wall connection reduces pipe bends and leaves less visible plumbing, improving bathroom appearance.
- Cleaning is simpler because the base is flush with the floor. Fewer gaps mean less dust and grime, making it more hygienic and low maintenance.
- The sleek design matches modern bathrooms, giving a contemporary look while remaining practical.
Disadvantages:
While the advantages are clear, there are also disadvantages that should be considered before installation.
- A P-trap toilet cannot be used in bathrooms with only a floor outlet. Installing one would require major plumbing changes.
- Retrofitting into older homes can be costly, since pipes may need rerouting and floor outlets sealed before installation.
What is an S-Trap Toilet?
An S-trap toilet is the traditional design most often seen in older Australian homes. Instead of connecting to the wall, the outlet pipe curves downward into the floor, forming an S shape. This style is practical and effective for homes with plumbing routed below the floor.
S-trap toilets are still widely used and readily available. If you have existing floor outlets, they remain the easiest and most cost-effective option. Unlike retrofitting a P-trap into an older bathroom, fitting a new S-trap toilet usually requires minimal changes.
How Does an S-Trap Toilet Work?
The principle of an S-trap toilet is the same as a P-trap: water remains in the curved section of the pipe to form a seal against sewer gases. The difference lies in the outlet direction, which goes directly into the floor.
This system works reliably in homes designed with floor plumbing. However, blockages can still occur, causing various toilet issues.
You can sometimes clear these blockages, but often a plumber is needed. Like a P-trap, the S-trap can be combined with a modern toilet flushing mechanism to improve efficiency.
Pros and Cons of Installing an S-Trap Toilet
When considering an S-trap toilet, it is important to weigh the strengths and weaknesses. While this design is reliable, it does have limitations compared to a P-trap.
Advantages:
S-trap toilets remain a popular option for good reason. These are the main benefits of choosing one.
- Fits seamlessly with bathrooms that already have floor outlets, avoiding costly plumbing changes.
- Easier and cheaper to install when replacing an existing S-trap toilet, since the plumbing is already aligned.
- Readily available and familiar to plumbers, making installation quick and hassle-free.
Disadvantages:
Despite their benefits, there are also reasons why some people prefer to move away from S-traps.
- Harder to clean around the base, as exposed pipes on the floor can collect dirt and grime.
- Bulkier design looks less modern compared to a P-trap, making it less appealing for bathroom upgrades.
P-Trap vs S-Trap Comparison (Side-by-Side)
To make the differences easier to visualise, Let’s compare P-trap and S-trap toilets side by side. While both serve the same function, the way they connect to your plumbing can affect installation, cleaning, renovation flexibility, and overall bathroom design.
The table below breaks down the key differences at a glance, so you can quickly see which option suits your home best.
| Feature | P-Trap Toilet | S-Trap Toilet |
| Shape | Looks like the letter “S.” | Looks like the letter “P.” |
| Outlet position | Waste outlet connects horizontally into the wall | Waste outlet connects vertically into the floor |
| Common Use | Modern homes, full bathroom renovations, or new builds | Older Australian homes |
| Required Plumbing Layout | Wall outlet plumbing | Floor outlet plumbing |
| Ease of replacement | Easy if wall outlet already exists | Easy when replacing an existing S-trap |
| Cleaning access | Easier to clean due to flush-to-floor base | Harder to clean around exposed floor pipe |
| Renovation flexibility | High flexibility in bathroom upgrades | Limited flexibility without plumbing changes |
| Visual appearance | Sleek, modern, minimal visible pipework | Bulkier, more traditional look |
| Cost to change trap type | Can be expensive if converting from floor outlet | Affordable if keeping existing layout |
Looking at the comparison, the main takeaway is that neither option is “better” across the board. Ultimately, it comes down to how your bathroom’s plumbing system is established and what you are trying to achieve.
P-trap toilets tend to suit modern layouts and renovation projects where a clean, streamlined finish is a priority. Meanwhile, S-trap toilets remain a practical and reliable choice in homes with existing floor outlets, especially when replacing a toilet without changing the plumbing.
Final Verdict: Which One Should You Choose?
The choice between a toilet P-trap and an S-trap depends entirely on the layout of your bathroom plumbing. If your home has a wall outlet, the P-trap is the best option. But if your home has a floor outlet, the S-trap is the practical choice.
Attempting to fit the wrong trap type usually leads to unnecessary costs and complications.
When upgrading your bathroom, it is also a good idea to review other features. For example, pairing your new toilet with an updated toilet cistern can improve efficiency.
Additionally, knowing how to flush the toilet manually or turn off the water to the toilet will help you handle emergencies.
How to Identify the Type of Trap in Your Home
Start by checking around the base of the toilet or directly behind the pan. When the waste pipe runs horizontally into the wall, the toilet uses a P-trap. When the pipe drops straight down into the floor, it’s an S-trap.
In many older Australian homes, S-trap pipework is still visible at floor level, which makes identification quick and easy. P-trap toilets are more commonly seen in newer builds, where the pipework is hidden behind the pan to create a cleaner, more modern finish.
In some bathrooms, particularly newer or recently renovated ones, the trap may be fully concealed so visual inspection is not always possible. Checking the toilet’s model number or manufacturer specifications will usually confirm if it’s a P-trap or S-trap.
Some toilets also include an access panel that allows a plumber to inspect the outlet without removing the unit. Working out whether your toilet uses a P-trap or an S-trap is usually quite straightforward once you know where to look.
You don’t need to know pipe sizes or plumbing terms to identify it, simply look at if the outlet disappears into the wall or the floor.
Still uncertain about what type of toilet it is? A licensed plumber can quickly identify the trap type and ensure you choose the correct replacement toilet without risking installation issues.
Can I Convert S-trap to P-trap (or Vice Versa)?
In some situations, converting between an S-trap and a P-trap is possible, but it’s not always as simple as swapping a connector. The conversion process is generally straightforward when the toilet suite is designed with adaptability in mind.
Some modern toilets include optional bends or connectors that allow limited adjustment between floor and wall outlets. This can work when the outlet positions are already close and no major changes are needed to the drain itself.
Even in these cases, compatibility varies by model, so checking manufacturer specifications is essential.
However, conversion can be a complex adjustment. This usually happens when the waste outlet needs to be relocated from the floor to the wall or vice versa, which the process itself involves cutting into floors or walls, rerouting drainage pipes, and ensuring everything meets Australian plumbing standards. Therefore, professional installation is mandatory.
Furthermore, cost and complexity can vary widely and are influenced by factors such as how far the outlet needs to be moved, whether tiles, concrete, or wall linings need to be removed, access to existing pipework, as well as compliance and certification requirements.
For this reason, changing trap types is most practical during a full bathroom renovation, when plumbing work is already planned.
So, if you want a cost-effective and least disruptive option, then opt for sticking with the current trap type while replacing your existing bathroom’s toilet.
FAQ about P-Trap vs S-Trap Toilets
It is common for people to have questions before deciding between a P-trap and an S-trap. Below are some of the most frequently asked questions.
Are S-traps illegal in Australia?
S-traps are not illegal. They are still sold widely and remain common in many homes, particularly older ones. However, new builds more often use P-traps, since wall plumbing is increasingly standard.
Should I consult with professional plumbers about toilet traps?
Yes, professional advice is recommended. While identifying the trap type is straightforward, installation requires expertise. A licensed plumber will ensure your toilet trap and toilet cistern are installed correctly, reducing the risk of leaks or ongoing problems.
Do toilets have P-traps by default?
Yes, all toilets come with a trap, but the type depends on the design. Some are built as P-trap models for wall outlets, while others are S-trap models for floor outlets. Checking your plumbing layout before purchase ensures you get the correct one.
What is a toilet set-out?
Toilet set-out refers to the distance from the wall to the centre of the waste outlet. This measurement is critical as it determines whether a toilet will align correctly with the drain In Australia, common set-outs include 140mm, 160mm, and 180mm.
Always check your existing set-out before purchasing a new toilet to prevent gaps between the toilet and wall, misaligned connections, and installation delays or extra plumbing work.
Can I replace an S-trap toilet with P-trap without moving the drain?
In most cases, no. A P-trap requires a wall outlet, while an S-trap connects to the floor drain. Without relocating the drain, the toilet will not align correctly, seals may fail, and plumbing compliance issues may arise.
There are limited exceptions using offset connectors, but these only work in very specific situations and are not a universal solution.
If you’re considering switching from an S-trap to a P-trap, it’s best done as part of a full bathroom renovation since plumbing changes are already planned and budgeted.
Conclusion
Both P-trap and S-trap toilets work well, but the right choice depends on your bathroom setup. A toilet P-trap is best for wall outlets, while an S-trap is designed for floor outlets.
If you are unsure which trap is right for your bathroom, the experts at Neighbourhood Plumbing can help. From selecting the right trap to providing reliable toilet repair service, we offer complete plumbing service solutions.
So, if you have any plumbing problems, contact us today!
About the Author
From unclogging the toughest drains to repairing leaking toilets, Ricky is a seasoned plumber who has brought his craftmanship to homes across Melbourne. He is passionate about sharing plumbing tips just as much as he is about fixing your plumbing issues. So, when your taps or pipes begin leaking, you know who to call.
