Updated 16 Oct 2026bottle trap7 min read
What is a bottle trap?
Quick answer
A bottle trap is the round canister under a wash basin or sink that holds a little water to stop drain smells coming up the plug hole. PUB's Code requires every sink and basin to have a trap like this before its waste pipe, and HDB's home care guide says the bottle type is the common one under sinks and basins in flats.
How it works
Picture a short, wide jar standing upright under the basin. Inside it, a narrow tube from the plug hole reaches down almost to the bottom. Near the top of the jar, on one side, is the outlet to the wall or floor.
- 1Water from the basin runs down the inner tube into the bottom of the jar.
- 2The jar fills until the water reaches the outlet, then spills out to the waste pipe.
- 3When the tap stops, the jar stays full up to the outlet. The bottom of the inner tube is under that water.
- 4Gas from the waste pipe would have to push down through the water and up the tube to reach the room. It cannot, so there is no smell.
The bottom of the jar unscrews by hand. That is the bottle trap's main selling point: hair, sludge and dropped rings collect in the base, and you can empty it over a pail. The steps are in our sink choke guide.
Under PUB's Code, the basin's waste pipe then runs to a floor trap and joins it above that trap's own water seal. So a basin has two seals between you and the sewer: the bottle trap and the floor trap.
Bottle trap, P-trap or S-trap?
These names describe shape. P and S say which way the outlet goes, and a bottle trap can come in either version.
| Bottle trap | P-trap (U bend to the wall) | S-trap (U bend to the floor) | |
|---|---|---|---|
| Shape | Upright canister | Tube bent into a U, outlet sideways | Tube bent into a U, outlet down |
| Space needed | Least. Fits behind a pedestal or in a narrow vanity | More than a bottle trap | More than a bottle trap |
| Cleaning | Unscrew the base | Undo two nuts and lift the U out | Undo two nuts |
| Where it chokes | In the base, where hair and sludge settle | At the bottom of the bend | At the bottom of the bend |
| Seal loss | No special risk | No special risk | Unvented, more likely to siphon its water out |
For a bathroom basin, a bottle trap is the usual choice. It is neat and quick to empty.
For a kitchen sink, opinions differ, and we do not think there is a clear winner. HDB's guide says bottle traps are common under kitchen sinks too. A U or P trap has a smooth bend with no chamber for grease and food to settle in, but it takes more room and is more work to open. If your kitchen sink chokes often and the trap is full of grease every time, the trap type is not the main problem; the pipe beyond it usually is.
Are bottle traps illegal?
Not in Singapore. PUB's Code names them: a sink and washbasin must have "a fitting trap (or bottle trap)" at the outlet.
The idea comes from the United States. The International Plumbing Code says traps must not have interior partitions unless the partition is part of the fixture or made of approved corrosion-resistant material. A bottle trap's inner tube is a partition, so some US jurisdictions do not accept them. That rule does not apply here.
Sizes sold in Singapore
Bottle traps are sized by the pipe they connect to, in inches and millimetres. Singapore hardware shops list three combinations.
| Size | Inlet x outlet | Examples, October 2026 |
|---|---|---|
| 32mm | 1 1/4" x 1 1/4" | HardwareCity PVC bottle trap "for basin waste", $4.50. Vicplas BT32X32 |
| 40mm to 32mm | 1 1/2" x 1 1/4" | Vicplas BT40X32 |
| 40mm | 1 1/2" x 1 1/2" | Horme SHOWY UPVC, $2.67. HardwareCity Husky chrome plated brass, $28. Vicplas BT40X40 |
HardwareCity sells its 32mm trap as a basin part. Kitchen sinks vary, so measure rather than assume.
- 1Measure across the threaded tail under the basin, the part the trap screws onto.
- 2Measure the outside of the pipe going into the wall or floor.
- 3Check whether the old trap's outlet goes sideways into the wall or down into the floor.
- 4Take the old trap, or a photo with a ruler next to it, to the shop.
PUB's Code sets trap and waste pipe sizes for basins and sinks in a separate standard drawing, so we have not quoted a PUB size here.
Chrome or plastic
| PVC or UPVC | Chrome plated brass | |
|---|---|---|
| Part price | $2.67 to $4.50 at Horme and HardwareCity | About $28 for a 40mm one at HardwareCity |
| Looks | Plain white or grey | Made to be seen |
| Weak point | Thin plastic cracks if over-tightened or knocked | Plating corrodes at the joints in a humid bathroom |
| Best for | Inside a pedestal, cabinet or vanity | Wall-hung basins with the trap on show |
Both work the same way. Chrome is less likely to crack if a mop or a foot hits it. Plastic hidden in a cabinet does the job for less.
Hand tight only
Plastic nuts and bases crack when forced with a wrench. Tighten by hand until the washer seals, then run the tap to check for drips.
When to replace one
Cleaning fixes a slow basin. Replacement is for a trap that cannot hold water or cannot seal.
- It drips from the base or a joint even with a new washer seated flat.
- The plastic is cracked, or the thread is stripped so the base will not tighten.
- The chrome has corroded through at the joints.
- The connection to the wall or floor pipe is loose or has pulled out.
- You are changing the basin, and the new waste is a different size.
A smell that stays after you run the tap, with no drip, is not always the trap. It can be a loose joint at the wall, or the floor trap the basin drains into.
What replacement costs
Changing a bottle trap does not need a PUB Licensed Plumber. PUB lists installing a basin or sink, including its bottle trap, as work anyone can do.
| Job | Typical price (SGD) |
|---|---|
| Replace with a PVC bottle trap | $60 to $100 |
| Replace with a chrome bottle trap | $80 to $150 (estimate; depends on the trap) |
| New trap fitted during a basin choke visit | +$20 to $40 on the clearing price |
| Redo the full basin waste: waste, trap and wall joint | $150 to $280 |
If the basin is also choked, it is cheaper to change the trap during that visit. The plumber already has it off. See bottle trap replacement, the price breakdown, or wash basin choke.
WhatsApp us a photo of the trap and where it meets the wall or floor, 24/7. We reply with a price range, and the price is agreed before work starts. Workmanship carries a warranty of 1 week to 1 month depending on the job; the trap itself carries the maker's warranty.
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Frequently asked questions
Is a P-trap or bottle trap better?
For a bathroom basin, a bottle trap: it fits in less space and its base unscrews for cleaning. A P-trap has a smoother bend with no chamber for sludge to settle in, but needs more room and is more work to open.
How do I take apart a bottle trap?
Put a pail underneath and unscrew the bottom section anticlockwise by hand. Empty it, clean it, check the rubber washer, and screw it back clockwise, hand tight. Our sink choke guide has the full steps.
What is the standard size of a sink trap?
Singapore shops sell bottle traps in 32mm (1 1/4 inch) and 40mm (1 1/2 inch), plus a 40mm to 32mm version. HardwareCity sells the 32mm one for basin wastes. Measure the threaded tail under your sink before buying.
Why are bottle traps illegal?
They are not illegal in Singapore; PUB's Code names the bottle trap as an accepted trap for sinks and basins. The idea comes from US codes, which ban traps with internal partitions unless they meet certain conditions.
How much does it cost to replace a bottle trap in Singapore?
Typically $60 to $100 with a PVC trap and $80 to $150 with chrome. If a plumber is already clearing a basin choke, a new trap adds about $20 to $40. These are estimates; send a photo on WhatsApp for a range.
Do I need a licensed plumber to change a bottle trap?
No. PUB lists installing a basin or sink, including its bottle trap, as work that does not need a Licensed Plumber. Anyone can change it, though over-tightening a plastic trap is the usual way it cracks.
Get a price on WhatsApp
Send a photo or short video, your home type and postal code. We reply with a price range and the earliest slot.
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