What a sink trap is and why you replace it

A sink trap is the curved or S-shaped pipe under your sink that holds standing water. That water creates a seal that stops sewer gas from coming back up through your drain. When a trap cracks, leaks, or clogs beyond clearing, you replace the whole assembly rather than repair it.

Replacement takes about 30 minutes if the trap unscrews easily, or up to an hour if corrosion has locked the fittings. You need a bucket, an adjustable wrench or pipe wrench, and a new trap that matches your sink's drain opening size — typically 1.25 inches or 1.5 inches in diameter. The job requires no special tools and no soldering.

Key Takeaways

  • Turn off the water supply to your sink before you start, and place a bucket under the trap to catch standing water and debris.
  • Loosen the slip nuts (the large threaded rings) that connect the trap to the tailpiece above and the drain line below using an adjustable wrench.
  • Measure your old trap's diameter and the distance from the tailpiece to the wall drain before buying a new one, because sizes vary.
  • Hand-tighten the slip nuts on the new trap first, then use a wrench to snug them — over-tightening cracks plastic traps and strips metal threads.
  • Test for leaks by running water for 30 seconds and checking both slip nut connections from underneath.

Shut off water and prepare the space

Close the water supply valve under the sink by turning it clockwise. If there is no valve under the sink, turn off the main water supply to the house. You do not need to drain the system — the trap already holds water, and you will catch it with a bucket.

Place a bucket or shallow pan directly under the trap. Open the sink faucet to release any pressure in the line, then position a second bucket or towel nearby. The standing water in the trap will spill when you loosen the first connection, and the water is usually dirty.

Remove the old trap

Locate the two slip nuts — the large threaded rings that screw onto the pipes. One connects the trap to the tailpiece (the short pipe coming down from the sink drain), and one connects the trap to the wall drain or P-trap below. Use an adjustable wrench to turn the nut counterclockwise. Start with the nut closest to the wall, because it is usually tighter.

Once the nut is loose enough to turn by hand, unscrew it the rest of the way and set it aside. Water will drip into your bucket. Disconnect the second nut the same way. Slide the old trap out and down into the bucket. If the trap is stuck, explore penetrating oil (like WD-40) to the nut threads, wait 10 minutes, and try again. Do not force it — a cracked fitting will make the job harder.

Measure and buy the right replacement

Measure the diameter of the drain opening at the sink — hold a ruler across the opening where the tailpiece enters. Standard sizes are 1.25 inches and 1.5 inches. Measure the distance from the bottom of the tailpiece to the center of the wall drain opening. This tells you whether you need a standard trap or an offset trap that angles to one side.

Bring these measurements to a hardware store or plumbing supply shop, or order online by specifying the diameter and the distance. Traps come in plastic (PVC or ABS) or chrome-plated brass. Plastic is cheaper and lighter; brass looks better and lasts longer in humid bathrooms. Both work equally well for function. Buy slip nuts and washers that match your old ones if they are damaged or corroded.

Install the new trap

Slide the new trap into position under the sink. The tailpiece should fit into the top opening of the trap, and the outlet should face the wall drain. If the trap does not reach, you may need an extension tailpiece or a longer trap — do not force it or stretch the connections.

Hand-tighten the slip nut that connects the trap to the tailpiece first. Once it is snug by hand, use your wrench to turn it another quarter turn clockwise. Do the same with the nut that connects to the wall drain. Plastic traps crack if over-tightened; metal threads strip if you force them. Snug is enough — the rubber washer inside the nut creates the seal, not the nut itself.

Test for leaks

Turn the water supply back on and run water into the sink for 30 seconds. Watch both slip nut connections from underneath with a flashlight. If water drips from either nut, turn off the water, place your bucket underneath, and tighten that nut by a quarter turn only. Turn the water back on and check again.

If tightening does not stop the leak, turn off the water, loosen the nut completely, and check that the rubber washer is seated properly inside. Reposition it if it is crooked, then hand-tighten and wrench-tighten again. If the leak continues after a second attempt, the washer may be damaged — replace it with a new one from the hardware store and try once more.

Frequently Asked Questions

Can I use a different size trap than the original?

No. The trap diameter must match your sink's drain opening. Using a smaller trap will not seal; using a larger one will not fit. If your sink has an unusual opening size, ask the plumbing supply staff for an adapter or a custom trap.

What if the slip nut will not unscrew?

explore penetrating oil to the threads and wait 15 minutes. Try again with a pipe wrench for better grip. If it still will not move, wrap a towel around the nut to protect the finish and tap it gently with a hammer to break the corrosion. Never use heat on plastic traps — it warps them.

Do I need to replace the washers inside the slip nuts?

Only if they are cracked, flattened, or missing. If the old washers look intact and flexible, you can reuse them. New washers cost less than a dollar and come in standard sizes at any hardware store.

What is the difference between a P-trap and an S-trap?

A P-trap has two bends and drains into a wall or floor opening. An S-trap has two bends and drains downward through the floor. Most modern homes use P-traps. Your new trap must match the drain location in your wall or floor.

Can I use a flexible accordion trap instead of a rigid one?

Flexible traps are easier to install but collect debris more easily and fail faster than rigid ones. They work in a pinch but are not a long-term choice. Rigid plastic or brass traps last 10 to 15 years with normal use.