How to Replace a P-Trap Under a Sink (2026)
The P-trap is the U-shaped pipe under every sink that holds water to block sewer gases. If it's leaking, cracked, or the sink is draining slowly, replacement takes 15 minutes and costs under $15.
Replace a P-trap: (1) Turn off the water supply and clear out under the sink. (2) Put a bucket under the trap. (3) Unscrew the two slip joint nuts — one where the P-trap connects to the tailpiece (the straight pipe coming down from the drain) and one where the trap arm connects to the wall drain stub-out. The trap assembly comes out. (4) Take the old P-trap to the store to match the pipe diameter (1-1/4 inch for bathroom sinks, 1-1/2 inch for kitchen sinks). (5) Install the new trap: slip nuts hand-tight first, check that the trap arm slopes slightly toward the wall, then tighten 1/4 turn past hand-tight with pliers. Run water and check for leaks.
Frequently Asked Questions
What is a P-trap and why does it matter?
P-trap function and importance: (1) The P-trap is the curved section of pipe under every sink (and also under showers, tubs, and floor drains). It is shaped like the letter P on its side, with a U-shaped dip. (2) Function: the U-bend holds a standing column of water — typically 2–3 inches deep — that creates an airtight barrier between the living space and the drain system. Without this water seal, sewer gases (methane, hydrogen sulfide) travel up through the drain and into the room. (3) The water seal is maintained because fresh water replaces it every time the drain is used. In a drain that goes unused for weeks (vacation home, infrequently-used bathroom), the trap can dry out and allow odors into the space. Running the tap for a minute refills it. (4) P-traps also catch debris — jewelry, small items, and sediment collect in the U-bend, which is why a P-trap cleanout is the first step when a ring falls down the drain. (5) Code requires: every fixture drain must have a trap. An S-trap (the old vertical-exit style) is not permitted in new construction because the flow dynamics can siphon the trap seal dry.
How do I know if my P-trap needs to be replaced?
P-trap replacement signs: (1) Visible drip or leak from the trap joints — the slip joint fittings compress washers that wear out over time. A drip at either slip nut joint indicates the washer has failed. Tightening the nut sometimes helps; if the drip continues, the washer or the trap needs replacement. (2) Crack in the trap body — plastic P-traps (ABS or PVC) can crack from impact or age. A crack will drip continuously whenever water runs. (3) Slow drain that doesn't improve with cleaning — built-up grease, soap scum, and debris inside the trap can partially block it. If drain cleaning does not help and the trap looks old and rough-walled inside, replacement is easier than cleaning. (4) Smell of sewer gas — can indicate the trap is cracked (water seal leaks out) or the connection to the wall drain is loose and sewer gas is bypassing the water seal. (5) Corroded chrome trap — older bathroom sinks often have chrome-plated brass P-traps. These corrode from the inside out and develop pinhole leaks. Replace with plastic (ABS or PVC) or new chrome brass.
How do I replace a P-trap step by step?
P-trap replacement procedure: (1) Clear under the sink and place a bucket directly under the U-bend to catch the water in the trap. (2) Unscrew the slip nut connecting the top of the P-trap to the tailpiece (the pipe coming straight down from the sink drain body). Most slip nuts are plastic and can be turned by hand — if corroded, use channel-lock pliers with a rag to protect the finish. (3) Unscrew the slip nut at the wall end of the trap arm (the horizontal section that goes into the wall stub-out). The old trap assembly comes out. (4) Measure or take the old trap to the store: the inside diameter is what matters — 1-1/4 inch for bathroom sinks, 1-1/2 inch for kitchen sinks. Verify the trap arm goes into the wall at the correct angle. (5) Install the new trap: slip the new trap in place. Hand-tighten both slip nuts, then use pliers to go 1/4 turn past hand-tight. Tighten both nuts before checking alignment. (6) Check the trap arm angle: the trap arm (horizontal section) should slope slightly toward the wall — 1/4 inch drop per foot maximum. If it slopes toward the trap or is flat, adjust by rotating the trap or adjusting the wall stub-out extension. (7) Run hot water for 2 minutes and check all joints for drips.
What is the correct P-trap height and configuration?
P-trap installation specifications: (1) Height: the drain tailpiece (from the sink drain body down to the P-trap inlet) should be long enough that the P-trap sits below the wall drain stub-out. The trap arm must slope toward the wall drain, not upward. (2) Trap arm slope: maximum 1/4 inch drop per foot toward the wall stub-out. No more than 1 inch of total drop over the trap arm length. If the arm slopes too steeply, the trap can self-siphon and lose its water seal. (3) Tailpiece length: the trap inlet should be at least 4 inches below the bottom of the sink drain body, to give the P-trap enough vertical space. Extension tailpieces can be cut to length. (4) Wall stub-out depth: the trap arm goes 1–3 inches into the wall stub-out. An escutcheon plate covers the gap at the wall. (5) Double sinks: a center drain double-bowl kitchen sink uses a Y-fitting tee to join both sink tailpieces before the single P-trap. (6) Trap size: always match the P-trap diameter to the tailpiece and wall drain stub-out diameter. Mixing 1-1/2 inch and 1-1/4 inch with adapters is a leak waiting to happen.
Can I use a flexible accordion P-trap?
Accordion P-trap vs. rigid P-trap: (1) Accordion P-traps (the black or white ribbed flexible plastic ones) are available in hardware stores and are easy to install because they stretch and flex to fit many configurations. (2) However: the corrugated interior surface traps grease, soap, and debris much more readily than smooth-wall pipe. Clogs develop faster in accordion traps. Most plumbers advise against them for permanent installations. (3) Code status: accordion P-traps are not permitted under plumbing code in many jurisdictions for hidden or concealed drain installations. They are sometimes accepted for exposed under-sink use, but check your local code. (4) Recommendation: use rigid ABS or PVC P-trap parts. If the existing configuration is awkward (sink drain not aligned with wall stub-out), use adjustable J-bend pieces or offset adapters rather than an accordion trap. Most plumbing supply stores carry a range of slip-joint adapters to accommodate non-standard configurations. (5) If the existing accordion trap is not causing problems and your concern is replacing a leaking one: use rigid pipe for the replacement, even if it requires minor adjustment to fit.
Replace a P-trap: (1) Turn off the water supply and clear out under the sink. (2) Put a bucket under the trap.
Take the old P-trap to the hardware store — matching the diameter (1-1/4 inch bath vs. 1-1/2 inch kitchen) matters.
What you need
- Replacement P-trap kit (match diameter: 1-1/4” bathroom, 1-1/2” kitchen)
- Bucket
- Channel-lock pliers and rag
Step 1: Remove the old trap
Place a bucket under the U-bend. Unscrew the two slip nuts by hand or with pliers. The trap comes out; water in the bend spills into the bucket.
Step 2: Verify fit and install
Match the new trap to the tailpiece and wall stub-out diameters. Slip both nuts on loose, then tighten 1/4 turn past hand-tight with pliers.
Step 3: Check trap arm slope
The horizontal arm should slope slightly toward the wall (1/4 inch per foot maximum). Adjust as needed before final tightening.
Step 4: Test for leaks
Run hot water for 2 minutes. Check every joint while the water is running and for 30 seconds after you stop.
Related guides
- How to Fix a Slow Draining Sink — clearing partial clogs before replacing the trap
- How to Unclog a Kitchen Sink — kitchen drain blockage causes and fixes
- How to Fix a Leaking Pipe — other common drain pipe leak repairs
- Clear under sink and place a bucket
Clear out cabinet contents under the sink. Place a bucket directly under the U-bend of the P-trap to catch the water that will spill out when the trap is removed.
- Remove the old trap
Unscrew the slip nut where the P-trap connects to the tailpiece (the straight pipe coming down from the sink drain). Turn by hand or with channel-lock pliers and a rag. Unscrew the slip nut at the wall end of the trap arm where it enters the wall stub-out. The old trap assembly comes out; water in the U-bend spills into the bucket. Take the old trap to the hardware store to match the diameter: 1-1/4 inch for bathroom sinks, 1-1/2 inch for kitchen sinks.
- Install the new trap
Slip both nuts onto the new trap loosely. Position the trap between the tailpiece and the wall stub-out. Hand-tighten both slip nuts, then use pliers to go 1/4 turn past hand-tight. Do not overtighten plastic nuts — they crack and cause leaks. Tighten both nuts before checking alignment.
- Check trap arm slope and adjust if needed
The horizontal trap arm (the section going into the wall) must slope slightly toward the wall — no more than 1/4 inch drop per foot. An arm that slopes toward the trap, runs uphill, or is too long can self-siphon the water seal and cause sewer gas odors. Adjust by rotating the trap or using extension tailpiece pieces.
- Test for leaks
Run hot water for 2 minutes. Check every slip nut joint while water is flowing and for 30 seconds after stopping. A drip at a joint: tighten slightly with pliers (1/8 turn). If still dripping: remove and check that the slip nut washer is seated properly and not twisted.
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