P-Trap Replacement Under Sink: Step-by-Step Guide

Replacing the P-trap under a sink is one of the most manageable plumbing repairs a homeowner can do. No special tools are required, the parts cost $5–$15, and the job takes 15–20 minutes. Here’s exactly how to do it.

When to Replace the P-Trap

Replace when:
– The trap body is cracked or has a pinhole leak
– The slip-joint nuts are cracked and won’t seal even with new washers
– The chrome trap is corroded and developing leaks
– You’re renovating and want fresh plumbing components
– The existing trap configuration doesn’t match your new sink installation

Repair instead of replacing (if the trap body is intact):
– Loose slip-joint nuts — just tighten
– Worn washers — replace the $1–$2 washers without buying a new trap

What You Need

Parts:
– P-trap kit for your drain size: 1-1/4 inch (most bathroom sinks) or 1-1/2 inch (kitchen sinks)
– A complete kit ($5–$15) includes: J-shaped trap bend, trap arm (horizontal section), slip-joint nuts, and rubber washers

Verify your size before purchasing. Measure the outside diameter of the drain pipe, or bring the old trap to the hardware store.

Tools:
– Bucket or container (to catch trap water when disconnecting)
– Towels
– Channel-lock pliers (optional — most plastic assemblies tighten by hand)

Step-by-Step P-Trap Replacement

Step 1: Clear out under the sink
Remove everything stored under the sink. Place a bucket directly under the P-trap to catch water.

Step 2: Disconnect the trap arm from the wall
The trap arm is the horizontal section that goes into the wall drain stub-out. There may be a slip-joint nut where it enters the wall fitting — unscrew it counterclockwise. Some configurations use a slip-joint nut; others have a compression fitting or a push-fit connection.

Step 3: Unscrew the slip-joint nuts
Locate the two slip-joint nuts on the P-trap — one at the top (where the drain tailpiece enters the trap) and one at the trap arm connection. Turn counterclockwise. These are designed to unscrew by hand; use pliers only if they’re stuck.

Step 4: Remove the old trap
Once both nuts are loose, slide the trap free. Water will drain from the trap into your bucket. Set the old trap aside.

Step 5: Clean the pipe ends
Wipe the drain tailpiece and the wall stub-out with a cloth. Remove any old washer material, scale, or debris from the pipe ends.

Step 6: Assemble the new trap
Before connecting, slide the new slip-joint nuts onto the pipe ends with the threaded end facing the fitting (threads go toward the connection, not away). Then place the rubber washers inside.

Step 7: Connect the trap arm to the wall
Insert the trap arm into the wall drain stub-out. The trap arm should slope slightly downward toward the wall (about 1/4 inch per foot) so water drains freely. Slide the nut onto the wall fitting and hand-tighten.

Step 8: Connect the trap to the drain tailpiece
Position the curved trap section so its open end aligns with the trap arm. Connect the slip-joint nut at the drain tailpiece. Hand-tighten.

Step 9: Tighten all connections
Tighten each slip-joint nut an additional 1/4 turn with pliers. Don’t overtighten — that cracks plastic nuts.

Step 10: Test
Run water in the sink for 30 seconds. Check each connection for drips. Wipe connections dry and wait 30 seconds more — if they stay dry, you’re done.

Common Mistakes to Avoid

Forgetting the washer direction: The washer must sit inside the nut, compressed between the nut and the pipe fitting. If the washer falls out or gets placed wrong, the connection leaks.

Overtightening: Plastic slip-joint nuts crack under excessive torque. Hand-tight plus 1/4 turn is sufficient.

Wrong trap size: Using a 1-1/4 inch trap on a 1-1/2 inch drain (or vice versa) won’t seal correctly. Verify size before purchasing.

Trap arm pointing the wrong direction: The trap arm must slope downward toward the wall drain — if it slopes back toward the sink, water sits in the arm and can’t drain fully.

FAQ

Q: How do I replace the P-trap under my sink?
A: Put a bucket under the trap, unscrew the two slip-joint nuts (counterclockwise), remove the old trap, slide new nuts onto pipe ends with washers, connect new trap sections, hand-tighten plus 1/4 turn, test for leaks. 15–20 minutes total.

Q: What size P-trap do I need?
A: 1-1/4 inch for most bathroom sinks, 1-1/2 inch for kitchen sinks. Measure the outside diameter of the drain pipe under the sink or bring the old trap to the hardware store to match it.

Q: Do I need a plumber to replace a P-trap?
A: No — P-trap replacement is one of the most DIY-friendly plumbing repairs. No soldering, no pipe cutting, and no tools required for standard plastic assemblies. If the wall drain stub-out is damaged or the plumbing configuration is complex (garbage disposal, double basin), a plumber can help.

Q: How much does it cost to replace a P-trap?
A: $5–$15 for the parts (a complete PVC or chrome trap kit). If you hire a plumber, expect $75–$150 for the labor — it’s typically under 1 hour.

Q: Why does my new P-trap still leak?
A: Most likely causes: a washer was installed incorrectly or fell out during assembly, a nut wasn’t tightened sufficiently, or the trap arm isn’t properly seated in the wall stub-out. Disassemble the leaking connection, verify the washer is in place and seated correctly, reassemble and tighten.