What is a P-trap and why does it matter?

A P-trap is the curved section of drain pipe under every sink, shaped like a P on its side. Its job is to hold a small plug of water — the trap seal — that blocks sewer gas from rising up through the drain into your home. That is why every fixture has one and why a dried-out or missing trap smells of sewer. It is also the most common place a sink clogs, because the low bend collects debris, which makes the removable slip-joint P-trap the easiest clog access point in the house.

Can I replace a P-trap myself?

Yes — it is one of the most beginner-friendly plumbing jobs, needing no special tools and about 30 minutes. Modern PVC slip-joint traps assemble by hand: you loosen the plastic slip nuts, drop the old trap into a bucket, and fit the new one with its washers, hand-tightening the nuts. There is no gluing, no soldering and no permit. The only version that is harder is an old chrome or brass trap that has corroded onto the tailpiece, which may need pliers and patience, or a trap that is glued rather than slip-joint.

Which way do the P-trap washers face?

The beveled (tapered) edge of each nylon slip-joint washer points toward the joint it seals — that is, toward the pipe it slides onto, with the taper going into the fitting. Getting a washer backward is the single most common reason a freshly assembled trap drips. On a standard PVC kit the washers are symmetrical enough to be forgiving, but on tapered nylon washers, orientation matters: the cone points down into the connection. Hand-tighten the nuts; these joints seal on the washer, not on force.

Why is my new P-trap leaking?

Almost always a washer that is backward, missing or pinched, or a slip nut that is cross-threaded or overtightened. Take it apart, confirm each washer is present and oriented with its bevel toward the fitting, and make sure the pipe is seated squarely — not cocked at an angle — before you tighten. Slip nuts seal by hand-tightening plus a small nudge; cranking them with pliers deforms the washer and cracks the plastic nut, which makes the leak worse. Also check the trap has a slight downward slope toward the drain.

Should the P-trap have a slope?

Yes — the horizontal arm running from the trap to the wall drain should slope slightly downward toward the wall, about 1/4 inch per foot, so waste water drains fully and does not sit and clog. The trap bend itself holds the water seal, but the arm must fall toward the drain. If you assemble it dead level or, worse, tilted back toward the sink, water pools and the trap clogs quickly. Cut the tailpiece and arm to length so the trap sits at the right height with that gentle fall.

How to Replace a P-Trap Under a Sink: 30-Minute Fix

Written & researched by Priya Anand DIY & Tools Editor

Updated August 2026

Over-the-shoulder view of a person's hands tightening a fitting under a kitchen sink with a wrench, in soft early-morning light

Affiliate Disclosure

Some links on this page are affiliate links. As an Amazon Associate, we earn from qualifying purchases — at no extra cost to you. We do not buy, test, or physically handle the products we cover; our rankings come from aggregated owner reviews, ratings and expert consensus. Commissions never change our verdicts. How we rank · full disclosure.

Replacing a P-trap is one of the easiest plumbing jobs — about 30 minutes, $8 to $15 for a PVC kit, no special tools, no permit and no plumber. The P-trap is the U-bend under the sink that holds a water seal against sewer gas and is where most sink clogs collect. You loosen the slip nuts by hand, drop the old trap into a bucket, and fit the new one with its washers oriented correctly and a slight slope on the arm. The only harder case is an old corroded metal trap seized onto the tailpiece.

We never buy, test or physically handle the products we rank; recommendations come from aggregated owner reviews and expert consensus, described in how we rank. More at the DIY plumbing hub.

How to Replace a PVC Sink Trap — This Old House

Tools and materials

A P-trap kit that matches your pipe size (1-1/4 inch for bathroom sinks, 1-1/2 inch for kitchen sinks).
A bucket and towels — the trap is full of water.
Channel-lock pliers (for stubborn nuts), and a hacksaw if you need to trim the tailpiece or arm.
Basic hand tools — see best plumbing tools.

Wide view of a person's hands tightening a fitting under a kitchen sink with a wrench, in soft early-morning light

Step 1: Position a bucket and loosen the slip nuts

Slide a bucket under the trap — it holds a cup or two of water. Loosen the two slip nuts by hand (or with pliers if they are tight): one where the trap meets the vertical tailpiece from the sink, and one where it meets the horizontal arm going into the wall. Turn them counterclockwise. Water will drain into the bucket.

Step 2: Drop the old trap

Once both nuts are loose, pull the trap free and empty it into the bucket. This is your chance to clear a clog — most sink blockages are sitting right here in the bend. Note how the old trap was assembled: the slip nuts and washers, and how the arm entered the wall. Keep the old parts to match lengths.

Over-the-shoulder view of a person's hands tightening a fitting under a kitchen sink with a wrench, in warm evening lamplight

Step 3: Fit the new trap with washers oriented correctly

Slide a slip nut and then a nylon washer onto each pipe, with the beveled edge of the washer facing the joint — the taper points into the fitting it seals. Assemble the trap bend to the tailpiece and to the wall arm, keeping everything hand-loose at first so you can align it. Trim the tailpiece or arm with a hacksaw if the kit pipes are too long.

Step 4: Set the slope and tighten

Position the horizontal arm so it slopes slightly downward toward the wall — about 1/4 inch per foot — so water drains fully. Make sure each pipe is seated squarely in its fitting, then hand-tighten the slip nuts plus a small nudge. Do not crank them — these joints seal on the washer, and overtightening cracks the plastic nut and deforms the washer.

Low-angle view of a person's hands tightening a fitting under a kitchen sink with a wrench, in warm late-afternoon light

Step 5: Test for leaks

Put a stopper in and fill the sink, then release a full basin of water at once so the trap runs under real flow. Watch every joint with a dry finger or a paper towel underneath. A drip means a backward or pinched washer, or a nut that needs a touch more — or less — tightening. Run water for a minute and check again.

Common mistakes

Installing a slip washer backward, the top cause of a dripping new trap.
Overtightening the plastic slip nuts and cracking them.
Assembling the arm level or tilted back, so water pools and clogs.
Mismatching pipe sizes — bathroom (1-1/4 inch) versus kitchen (1-1/2 inch).

When to call a plumber

This is DIY for nearly everyone, with no permit. Call a plumber if the pipe going into the wall is old, corroded metal that crumbles when you loosen the nut, if there is no trap arm or the drain stub in the wall is damaged, or if you find the trap was glued solid rather than slip-joint and the connection at the wall will not come apart cleanly. Reworking the drain stub inside the wall is beyond a simple trap swap.

How to Replace a P-Trap Under a Sink