S-Trap vs P-Trap Toilet Bowl: How to Match Yours
TL;DR: S-trap vs P-trap is not a choice you get to make. Your floor already made it S-trap if the waste pipe drops into the floor, P-trap if it goes back into the wall. The decision you actually have to get right is the number beside the letter: the setout, in millimetres. Get the letter right and the number wrong and the bowl still will not fit.
1. Introduction: the letter is not the decision
Quick Answer: Almost every guide to S-trap vs P-trap frames it as a decision between two products. In a house that already exists, it is not. The concrete decided it years ago. Your job is to read what was decided and then match the setout measurement to it.
Search "S-trap vs P-trap" and you will find a lot of pages asking which one is better. It is the wrong question for anyone with a bathroom already built.
A toilet's trap type describes where its waste outlet points. That has to line up with where your drain actually is. If the drain drops through the floor slab, no amount of preferring the other type will help you.
So the useful version of the question is not "which should I buy". It is "which do I have, and what is the distance". Both answers are visible in about half a minute, without tools, and together they narrow a 47-model water closet range down to the handful that will actually bolt down.
This guide covers how to read your existing setup, what the codes on Malaysian product listings mean, and what it costs when the match is wrong. The video below shows the offset situation that catches people out.
Watch: P-trap installation
A plumber works through what happens when the outlet and the drain do not line up, and how the connection is made good.
Source: P-Trap Installation: Drain Doesn't LINE UP with Bathroom Sink Pipe — The Building Expert
2. What the two letters actually describe
Quick Answer: Both traps are a bend that holds a plug of water to stop drain smells entering the room. The difference is only direction. An S-trap sends waste down through the floor. A P-trap sends it back horizontally into the wall. Same job, different exit.
Every toilet has a trap. It is the curved section built into the porcelain, and it always holds a little standing water. That water is the seal between your bathroom and the drain. Without it the room smells.
The letters are just shape descriptions from the side view:
- S-trap. The waste path curves down, round and down again, roughly tracing an S. It leaves the bowl vertically and enters a pipe in the floor.
- P-trap. The waste path curves down, round and then runs level, tracing a P lying on its back. It leaves the bowl horizontally and enters a pipe in the wall.
That is genuinely the whole distinction. Everything else people argue about in S-trap vs P-trap comparisons follows from those two directions. A wall exit needs a wall with a drain in it. A floor exit needs a slab that has been cored or cast for it.
Which is why the comparison is settled before you start shopping. You are not picking a direction. You are reading one. The close-coupled WC sets that make up most of the market come in both, and they are not interchangeable.
Key takeaway: S-trap goes down into the floor, P-trap goes back into the wall. The trap holds the water seal in both cases — only the exit direction changes.
3. How to tell which one you have in thirty seconds
Quick Answer: Look at the back of the pan where it meets the floor. If nothing visibly leaves the toilet and the base sits flush on the tiles, it is an S-trap. If a short pipe runs from the back of the pan into the wall, it is a P-trap. Then measure the setout.
You do not need to lift anything or open anything. Two checks:
- Find the exit. Kneel beside the pan and look at where the porcelain meets the floor and the wall behind it. A visible horizontal pipe or a covered stub going into the wall means P-trap. Nothing visible, base sealed to the floor, means the outlet drops straight through the tiles S-trap.
- Measure the setout. For an S-trap, measure from the finished wall behind the pan to the centre of the floor outlet. For a P-trap, measure from the finished floor up to the centre of the wall outlet. Record it in millimetres.
Measure from the finished wall, not the skirting. A skirting board or a tile lip will throw the number out by enough to matter, and the setout is not a figure with room to be roughly right.
If the existing toilet is still in place and you cannot see the floor outlet, the centre of the two floor bolts is a close proxy for it. Photograph the back of the pan and the base while you are down there — it is the single most useful thing to bring to a showroom.
Key takeaway: Visible pipe into the wall means P-trap. Nothing visible means S-trap. Then one measurement in millimetres, taken from the finished wall or floor.
Got your letter and your number?
That is everything needed to shortlist properly — filter the water closet range by trap type →
4. How to read the trap code on a Malaysian product listing
Quick Answer: Malaysian toilet listings carry a code like "S-250mm" or "P-180mm" in the product name. The letter is the trap type and the number is the setout in millimetres. Once you can read it, the product title alone tells you whether a model can fit your bathroom.
This is the piece most S-trap vs P-trap explainers leave out, and it is the practically useful part. Local listings put the answer in the title.
| Code seen in the title | Trap type | What the number means | Fits your bathroom if… |
|---|---|---|---|
| S-150mm | S-trap, floor outlet | Wall to outlet centre | Your floor outlet sits 150mm off the wall |
| S-200mm | S-trap, floor outlet | Wall to outlet centre | Common in tighter or older layouts |
| S-250mm | S-trap, floor outlet | Wall to outlet centre | The most widely stocked S-trap setout |
| S-300mm | S-trap, floor outlet | Wall to outlet centre | Outlet sits further out from the wall |
| P-180mm | P-trap, wall outlet | Floor to outlet centre height | Your wall outlet centres 180mm above the floor |
Compiled from trap codes appearing in Big Bath's water closet product titles. Big Bath stocks S-trap rough-ins at 150mm, 200mm, 225mm, 250mm, 275mm and 300mm, plus P-trap at 180mm.
Note the two numbers are measured along different axes. An S-trap figure runs horizontally from the wall. A P-trap figure runs vertically from the floor. Reading one as the other is a common and expensive mix-up.
Key takeaway: Letter equals trap type, number equals setout in millimetres. S-trap numbers measure out from the wall; P-trap numbers measure up from the floor.
5. Which trap type Malaysian ranges are actually built around
Quick Answer: S-trap dominates the Malaysian range and P-trap is the minority option, which is the opposite of what British and American guides suggest. That reflects how local bathrooms are built: waste runs through the slab far more often than through the wall.
Counting trap codes across a stocked range shows the split clearly.
| Trap code | Share of the sample | Models |
|---|---|---|
| S-250mm |
|
6 |
| S-300mm |
|
4 |
| P-180mm |
|
4 |
| S-200mm |
|
1 |
| S-150mm |
|
1 |
Counted from the first sixteen product titles listed in Big Bath's water closet collection of 47 products. A sample of one collection page, not a market-wide share.
Twelve of the sixteen are S-trap. That matters when you are shopping: if you have a P-trap bathroom, your shortlist is genuinely narrower, and it is worth confirming stock before travelling rather than assuming the floor model can be swapped. Style ranges such as rimless bowls appear in both traps, but not every finish does.
Key takeaway: S-trap is the default here and 250mm is the most common setout. P-trap buyers should check availability early, not late.
6. Why "S-traps are banned" does not apply to your bathroom
Quick Answer: A lot of English-language plumbing advice says S-traps are prohibited. That refers to a specific American and Australian restriction on unvented S-traps under sinks and basins, not to floor-outlet toilet pans, and it is not the rule Malaysian homes are built to.
This one causes real confusion, because the warning sounds absolute and it is repeated everywhere.
The restriction those codes describe targets a genuine problem: an unvented S-trap on a basin or sink can siphon its own water seal away as the water drains, leaving the room open to the drain. The fix in those countries was to require venting and to standardise on P-traps for those fixtures.
A floor-outlet toilet is a different case. The pan carries its own trap, the cistern refills the seal on every flush, and the branch is vented as part of the building's stack. That is why S-trap toilets are normal, code-compliant and widely sold across Malaysian sanitary ware ranges rather than being a legacy oddity.
The practical upshot: do not let imported advice talk you into converting a working floor outlet to a wall outlet. That conversion means opening the slab or building out a false wall, and it solves a problem you did not have.
Key takeaway: The "S-traps are banned" warning is about unvented basin and sink traps overseas. It is not a reason to re-plumb a working Malaysian toilet.
Not sure whether your outlet can take the model you want?
Send a photo of the pan base and your setout measurement, and get it checked before you buy see the full catalogue first →
7. What a mismatch actually costs you
Quick Answer: Getting the trap type wrong is not a small error it means the bowl cannot connect at all. Getting the setout wrong by a small margin is sometimes correctable with a connector; by a large margin it means tiles come up.
The two failure modes are not equally bad, and it helps to know which you are facing.
| What went wrong | What happens on installation day | Fixable without hacking? |
|---|---|---|
| Bought P-trap, have floor outlet | Outlet points at the wall, drain is in the floor. No connection possible. | No — wrong product, return it |
| Bought S-trap, have wall outlet | Outlet points at the slab, drain is in the wall. No connection possible. | No — wrong product, return it |
| Setout short by a small margin | Pan sits proud of the wall with a visible gap behind the cistern. | Often — offset connector or a shift |
| Setout out by a large margin | Bolt holes and outlet cannot both line up. Pan will not seat. | Rarely — usually means lifting tiles |
| Measured from the skirting | Everything looks right on paper and is out by the skirting thickness. | Sometimes — depends how far out |
Compiled description of common installation outcomes for Malaysian toilet replacements. Describes typical scenarios as a planning aid, not measured failure rates.
The top two rows are the reason the S-trap vs P-trap question gets asked at all, and they are entirely avoidable with one look behind the pan. The bottom three are why the number matters as much as the letter.
Connectors exist for modest discrepanciesseveral ranges ship with a P-to-S connector included but they buy you a small adjustment, not a free pass. A replacement flush valve is a cheap afternoon; a mis-set pan is a tiler.
Key takeaway: Wrong trap type means the toilet goes back. Wrong setout means either a connector or a tiler, depending on how far out you are.
8. S-trap and P-trap side by side
Quick Answer: On the things buyers usually care about flushing performance, cleaning, noise, model choice the two traps are close to identical. They differ on installation flexibility and on how the base looks, and that is about it.
Set the real differences against the imagined ones.
| Point of comparison | S-trap | P-trap |
|---|---|---|
| Waste direction | Down through the floor | Back through the wall |
| Measurement taken | Wall to outlet centre | Floor to outlet centre |
| Room to shift the pan | Limited — the slab is fixed | A little more, along the wall |
| Visible pipework | None — base sits on the floor | Short stub, usually concealed |
| Flushing performance | Set by the flush design, not the trap | Set by the flush design, not the trap |
| Ease of cleaning | Depends on rim style, not the trap | Depends on rim style, not the trap |
| Choice available locally | Wide, across several setouts | Narrower, typically one setout |
Compiled comparison based on Big Bath's water closet range and standard installation practice in Malaysia.
Two rows say the same thing twice on purpose. Flushing and cleaning are the qualities people most often attribute to the trap, and neither has anything to do with it they follow from the flush system and the rim design.
Key takeaway: Neither trap flushes better or cleans easier. Judge those on the flush system and the rim, and let the plumbing decide the trap.
9. Conclusion: read the plumbing, then shop
S-trap vs P-trap looks like a product comparison and behaves like a site survey. The honest answer to "which is better" is that neither is, and that the question has already been answered by whoever poured your floor.
What is left is a short, ordinary sequence. Look behind the pan and find the exit. Measure the setout from the finished wall or the finished floor, in millimetres. Read the code in the product title and match both parts of it. Then choose on the things that genuinely vary between modelsthe flush system, the rim, the seat, the finish.
Do that and the trap question disappears entirely, which is the point. It is a compatibility check, not a preference. The models that pass it are the only ones worth comparing, and everything after that is a normal purchase from a bathroom specialist who can confirm the fit before it is delivered.
10. Frequently asked questions
What is the difference between an S-trap and a P-trap toilet?
Only the direction the waste outlet points. An S-trap leaves the bowl vertically and drains into a pipe in the floor. A P-trap leaves horizontally and drains into a pipe in the wall. Both hold a water seal that stops drain smells entering the bathroom.
How do I know if my toilet is S-trap or P-trap?
Look at the back of the pan where it meets the floor and wall. If a pipe runs from the pan into the wall, it is a P-trap. If nothing is visible and the base sits flush on the tiles, the outlet drops through the floor, so it is an S-trap.
What does S-250mm mean on a toilet listing?
It means an S-trap pan with a 250mm setout the distance from the finished wall behind the toilet to the centre of the floor outlet. A P-180mm listing means a P-trap whose wall outlet centres 180mm above the finished floor.
Can I replace an S-trap toilet with a P-trap one?
Not directly. The drain would have to be moved from the floor to the wall, which means opening the slab or building out a false wall. Unless the bathroom is being stripped anyway, match the trap type you already have.
Are S-trap toilets illegal in Malaysia?
No. The prohibition often quoted online comes from American and Australian rules about unvented S-traps on basins and sinks, not floor-outlet toilet pans. S-trap toilets are standard and widely stocked in Malaysia.
What happens if the setout measurement is wrong?
A small discrepancy can often be taken up with an offset connector or by shifting the pan slightly. A large one means the outlet and bolt holes will not line up, and correcting it usually means lifting tiles and moving the drain.
Check the fit before you buy, not after
Send a photo of the back of your toilet and your setout measurement, and a Big Bath specialist will tell you which models actually fit before anything is ordered or delivered.
Get your trap and setout checked
