What you are replacing and why it fails

The kitchen drain under your sink is a P-trap — a U-shaped pipe that holds water to block sewer gas from coming back up. It connects to the tailpiece (the pipe coming straight down from the sink) and then to the wall drain. Over time, the P-trap corrodes, cracks, or develops slow leaks that pool under the cabinet. Replacing it is a straightforward job that takes 30 to 45 minutes and costs $15 to $40 in parts.

You will know it is time to replace when you see water pooling under the sink after you drain it, smell sewer gas, or notice the pipe itself is visibly cracked or has white mineral buildup that will not clean off. If the leak is only at a connection point (where two pieces screw together), you may be able to tighten or reseal it first — but if the pipe body itself is damaged, replacement is the only fix.

Key Takeaways

  • A P-trap replacement requires only a bucket, adjustable wrench, and a new P-trap kit that matches your sink's drain size (usually 1.5 inches for kitchen sinks).
  • Turn off the water supply to your sink, place a bucket under the trap, and unscrew the two slip nuts connecting the trap to the tailpiece and wall drain.
  • Measure the distance from the tailpiece to the wall drain before you buy a new trap, because P-traps come in different heights and arm lengths.
  • Wrap plumber's tape around the male threads of the new trap before screwing it in, then hand-tighten the slip nuts and check for leaks before you close the cabinet.
  • If the wall drain opening is cracked or the tailpiece is damaged, you will need to replace those pieces too — this is when to call a plumber.

Gather your tools and materials

You need very little to do this job. Collect an adjustable wrench (or two, if you have them), a bucket or shallow pan, a flashlight, plumber's tape (also called PTFE tape or thread seal tape), and a new P-trap assembly. The trap should match your sink's drain size — most kitchen sinks use 1.5-inch traps, but some older homes use 1.25 inches. Bring a photo of your current trap to the hardware store if you are unsure, or measure the diameter of the pipe with a ruler.

You may also want a rag, a small bowl of water to test the seal, and a headlamp if your under-sink lighting is poor. Do not buy a trap yet — first measure your setup so you know what height and arm configuration you need.

Measure before you buy

P-traps come in different sizes because the distance from your sink's tailpiece to the wall drain varies. Measure from the center of the tailpiece opening to the center of the wall drain opening. Write down both the vertical distance (how far down the wall drain sits) and the horizontal distance (how far out from the wall the tailpiece is). Most hardware stores stock standard 1.5-inch traps in a few common configurations, but if your measurements are unusual, you may need to special-order or buy an adjustable trap.

Also check whether your current trap has a cleanout plug at the bottom of the U-bend — some do, some do not. If yours does and you want to keep that feature, note it when you shop. Take a photo of the underside of your sink with your phone so you can reference it while you are at the store.

Disconnect the old trap

Place your bucket under the trap to catch any remaining water. Using your adjustable wrench, loosen the slip nut (the large hexagonal nut) that connects the trap to the tailpiece — this is the nut closest to the sink. Turn it counterclockwise by hand once it is loose enough. Then loosen the slip nut connecting the trap to the wall drain (the one closest to the wall). Again, turn counterclockwise by hand.

Once both nuts are loose, you can unscrew them the rest of the way by hand and slide the old trap out. Some water will drip — that is normal. If the trap is stuck, spray the slip nuts with penetrating oil and wait 10 minutes, then try again. Do not force it or you may crack the tailpiece or wall drain.

Install the new trap

Before you screw anything in, wrap plumber's tape around the male threads (the threads on the ends of the new trap that will go into the slip nuts). Wrap it clockwise three to four times, pressing it down as you go. This tape seals the connection and prevents leaks. It is cheap insurance and takes 30 seconds.

Slide the new trap into place, aligning the top opening with the tailpiece and the bottom opening with the wall drain. Hand-tighten the slip nut on the tailpiece first, then hand-tighten the slip nut on the wall drain. Once both are hand-tight, use your wrench to tighten each one a quarter turn more — no more than that. Over-tightening can crack the trap or strip the threads. The goal is snug, not vice-grip tight.

Test for leaks

Fill your sink with water and let it drain while you watch underneath. If water drips from either slip nut, tighten that nut a quarter turn more with your wrench and test again. If it still leaks after a second quarter turn, stop — you may have a thread problem. Turn the water off and loosen the nut to check that the plumber's tape is still in place and wrapped correctly.

If the leak is coming from the trap body itself (not from a connection), the trap is defective and needs to be exchanged. Once the trap holds water without dripping for a full minute, you are done. Close the cabinet and check again after an hour to make sure no slow leak has developed.

When to call a plumber instead

If the tailpiece (the pipe coming down from the sink) is cracked or corroded, or if the wall drain opening is damaged, replacing just the trap will not solve the problem. You will need those pieces replaced too, and that work is easier with a plumber because it may involve opening the wall or disconnecting the sink itself. The same applies if you have a double sink and the two drains share a single trap — that configuration is more complex to disassemble and reassemble.

Also call a plumber if you cannot loosen the old slip nuts after spraying them with penetrating oil and waiting, or if you crack the tailpiece or wall drain while removing the old trap. Trying to force a stuck connection can cause damage that costs more to fix than hiring help from the start.

Frequently Asked Questions

Do I need to turn off the water supply?

No — the P-trap holds standing water, not flowing water. You do not need to shut off the supply. Just make sure the sink is empty before you start, and place a bucket underneath to catch the water that drains out when you loosen the trap.

What if I cannot get the slip nuts to tighten and stop leaking?

The threads may be stripped or the plumber's tape may not be seated correctly. Loosen the nut completely, remove the trap, and rewrap the male threads with fresh tape, pressing it down firmly. If it still leaks after reinstalling, the trap itself may be defective — exchange it for a new one.

Can I use regular tape or caulk instead of plumber's tape?

No. Plumber's tape is made to seal threaded connections and will not harden or crack. Regular tape or caulk will fail under water pressure and will not create a watertight seal. Plumber's tape costs a dollar or two and lasts for years, so it is worth buying the right material.

How long does a P-trap usually last?

Most P-traps last 10 to 15 years, depending on your water quality and how often the drain is used. Hard water and frequent drain cleaning can shorten that lifespan. If your trap is more than 15 years old and you see any corrosion or discoloration, replacing it now can prevent a surprise leak later.

What should I do with the old trap?

If it is metal, you can take it to a scrap metal recycler. If it is plastic, check your local trash and recycling rules — some programs accept it, some do not. Your hardware store may also take it back. Do not pour anything down the drain before you remove the trap, and do not leave it sitting under the sink for more than a day, as any remaining water will start to smell.