Short answer
Buy a 1-1/4 in P-trap for a bathroom sink and a 1-1/2 in P-trap for a kitchen sink. PVC is the easy, low-cost choice for most cabinets; chrome-plated brass looks better under an open pedestal or console sink. A kit with the J-bend, trap arm, slip nuts and washers covers most swaps. Skip corrugated flexible traps where you can: their ridges catch debris, and some local codes do not allow them.
What a P-trap does
Look under a sink and the pipe dips down, curves back up, and runs sideways into the wall. That dip is the trap. It always holds some water, and that water seal is what stops sewer gas from rising out of the drain. The ICC summarizes the International Plumbing Code rule: every fixture trap needs a liquid seal of at least 2 in and no more than 4 in. Local codes vary, so check yours.
The trap also catches things. Rings, earring backs and most grease and hair clogs end up in the curved section, which is why opening the trap is a standard unclogging step.
Parts of a P-trap
| Part | What it does |
|---|---|
| Tailpiece | The straight pipe from the sink drain down into the trap. Not always part of the trap kit. |
| J-bend | The U-shaped section that holds the water seal. It comes off when you clean the trap. |
| Trap arm | The bend that leaves the J-bend and runs into the drain pipe in the wall. |
| Slip nuts | Plastic or metal nuts that clamp each joint. Hand tight plus a little more. |
| Slip washers | Tapered rings inside each slip nut that make the seal. The taper faces the joint. |
Sizes: 1-1/4 or 1-1/2 in
Sink traps come in two sizes. HomeGuide lists the standard: 1-1/4 in for bathroom (lavatory) sinks and 1-1/2 in for kitchen sinks. Match the trap to your tailpiece. If the wall pipe is 1-1/2 in and the tailpiece is 1-1/4 in, a reducing washer or a 1-1/2 x 1-1/4 in trap handles the change. The sink drain size guide has the full chart.
P-trap kit types
-
01Kitchen
PVC P-trap kit, 1-1/2 in
Best for: kitchen sinks inside a cabinet
- Size
- 1-1/2 in
- Material
- PVC (white)
- Joints
- Slip nuts and washers
- J-bend, trap arm, slip nuts and washers in one kit
- Cuts with a hacksaw or tubing cutter if the arm is too long
- Low cost and does not corrode
-
02Bathroom
PVC P-trap kit, 1-1/4 in
Best for: bathroom vanity sinks
- Size
- 1-1/4 in
- Material
- PVC
- Joints
- Slip nuts and washers
- Matches the standard bathroom tailpiece
- Some are sold as 1-1/2 x 1-1/4 in with a reducing washer for a larger wall pipe
- Read the size on the listing twice; the two sizes look alike
-
03On show
Chrome-plated brass P-trap
Best for: pedestal, console and wall-hung sinks where the trap is visible
- Size
- Usually 1-1/4 in
- Material
- Chrome-plated brass
- Finish
- Chrome, sometimes other colors
- Looks finished under an open sink
- Tube wall thickness varies, so check the gauge on the listing
- Some kits include an escutcheon (wall flange) to cover the hole
-
04Check code
Flexible (accordion) P-trap
Best for: awkward offsets, only where your local code allows
- Size
- 1-1/4 or 1-1/2 in
- Material
- Corrugated plastic
- Watch for
- Ridges catch debris
- Bends to reach a drain that does not line up
- Corrugated walls catch grease and hair more than smooth pipe
- Some local codes do not allow corrugated traps; check before you buy
Materials: PVC, ABS or chrome brass
- PVC (white): the most common sink trap. Inexpensive, does not corrode, easy to cut. Avoid boiling water down a PVC drain; very hot tap water is fine.
- ABS (black): a similar plastic used in some regions and older homes. Slip joints connect either one, but glued joints need the right cement for the material, so match what is already there.
- Chrome-plated brass: for traps on show. Tighten the slip nuts gently; overtightening crushes thin-wall tube.
Flexible traps: why most plumbers avoid them
A flexible or accordion trap can bridge a gap when the drain and wall pipe do not line up. The ridges inside are the problem: they catch grease, food and hair, so the trap clogs more often than smooth pipe. Some local codes do not allow corrugated traps at all, so check your local code before you use one. A standard trap with an extension tube or a trap arm cut to length usually solves the same problem.
Installing a P-trap
- Dry fit first. Slide the slip nuts and washers on, push the pieces together, and check that the trap arm reaches the wall pipe without strain.
- Keep the arm sloping down toward the wall. Water has to run downhill all the way. Your local code sets the exact slope and maximum arm length.
- Washer taper toward the joint. The tapered side of each slip washer faces the fitting it seals against.
- Hand tight, then a little more. Plastic slip nuts crack if you crank them with pliers.
- Test. Fill the sink, pull the stopper, and run a dry paper towel around each joint.
Also useful
Cleaning a P-trap
Most kitchen clogs are grease and food in the trap (The Home Depot). Put a bucket underneath, unscrew both slip nuts, lower the J-bend, and clean it out. The full steps are in how to unclog a kitchen sink and how to unclog a bathroom sink. A smelly sink can mean a dry trap: see sink drain smells.
If your trap drops straight into the floor instead of turning into the wall, you may have an S-trap: read S-trap vs P-trap.
Questions people ask
What does a P-trap do?
It holds water in its curved section. That water seal blocks sewer gas in the drain line from coming up into the room. The International Plumbing Code calls for a trap seal at least 2 inches and no more than 4 inches deep.
What size P-trap do I need?
Bathroom sinks use a 1-1/4 inch trap and kitchen sinks use a 1-1/2 inch trap. Match the trap to your tailpiece and to the pipe coming out of the wall. Reducing washers and 1-1/2 by 1-1/4 inch adapters exist when the two do not match.
Is a PVC or metal P-trap better?
PVC is inexpensive, does not corrode and is easy to cut and fit, so it is the usual choice inside a cabinet. Chrome-plated brass looks better where the trap is on show, such as under a pedestal sink. Check that the material matches what your local code allows and what the drain line is made of.
Are flexible P-traps allowed?
It depends on where you live. Some local codes do not allow corrugated or accordion traps, and their ridges tend to catch grease and hair. A standard smooth trap is the safer choice. Check your local code or ask a licensed plumber.
How do I clean a P-trap?
Put a bucket under it, unscrew the two slip nuts by hand or gently with pliers, and lower the J-bend. Empty it, clean out the gunk with a gloved finger or a brush, check the slip washers, and refit it hand tight plus a little more. Run water and check for drips.
Why does my sink smell even with a P-trap?
The trap may have dried out from lack of use, so the water seal is gone. Run water for a minute to refill it. Other causes include gunk in the trap or overflow channel and venting problems.
Sources
Last reviewed October 12, 2026. Parts, sizes and listings change; check the product details before you buy, and follow the maker’s instructions.