To clean the pipes under a sink, put a bucket under the P-trap, loosen its two slip nuts by hand, remove and empty the trap, scrub it and the trap arm, then reassemble with the washers seated and the nuts hand-tight plus a small turn. For a bathroom sink, pull and clean the pop-up stopper first. Run water to check for leaks and to refill the trap's water seal.
- Most slow sinks are blocked within the first half metre: the stopper, the trap or the trap arm.
- The trap exists to hold a water seal against sewer gas, so it must be refilled after cleaning.
- Plastic slip nuts need only hand-tight plus a small turn; overtightening cracks them or distorts the washer.
- Never open a trap that may hold a chemical drain opener.
- If the trap is clean and the sink is still slow, the clog is in the wall or beyond, and the next tool is an auger.
01 /What are the pipes under a sink, and why is there a trap?
The pipes under a sink are a short chain of parts that carry water from the basin into the drain in the wall, with a U-shaped trap in the middle that always holds some water. That water seal blocks sewer gas from coming up into the room, which is why every fixture has one and why the National Plumbing Code of Canada treats traps and venting as essentials rather than extras.
| Part | What it does | What usually clogs it |
|---|---|---|
| Strainer or pop-up stopper | Catches solids; a bathroom stopper opens and closes the drain | Hair and soap wound round the stopper |
| Tailpiece | Straight pipe down from the sink | Soap film; food in kitchen sinks |
| P-trap | The U-bend that holds the water seal | Grease, food, hair, dropped objects |
| Trap arm | Near-level pipe from the trap into the wall | Grease and sludge settling along its length |
| Continuous waste (double sinks) | Joins both bowls to a single trap | Food at the tee where they meet |
| Dishwasher or disposal connection | Brings dishwasher water in above the trap | Food particles; a knockout plug left in a new disposal |
Older houses sometimes have an S-shaped trap that drops straight into the floor instead of turning into the wall. That design can siphon its own water seal, and current codes do not accept it in new work. If yours is an S-trap and it keeps smelling, a plumber can advise on a change.
02 /What do you need before you start?
- A bucket or basin that fits under the trap, and old towels.
- Rubber gloves and eye protection; trap sludge splashes.
- A bottle brush on a wire and an old toothbrush.
- Slip-joint pliers, with a cloth to protect plastic nuts, only if a nut will not turn by hand.
- Spare slip-joint washers in the right size, in case the old ones are flattened or cracked.
- A flashlight, and a clear cabinet: take everything out first.
03 /How do you clean a P-trap, step by step?
- Empty the sink
Bail out standing water with a cup so less of it ends up in the bucket and on the floor.
- Put the bucket in place
Centre it under the U-bend, with towels around it.
- Loosen the slip nuts
Turn both nuts on the trap counter-clockwise by hand. If one is stuck, wrap it in a cloth and use slip-joint pliers gently; plastic nuts crack if squeezed hard.
- Remove and empty the trap
Lower it carefully and tip the contents into the bucket. Bag the solids for the garbage rather than washing them down another drain.
- Scrub the parts
Clean the trap and tailpiece with a bottle brush, dish soap and hot water, in a laundry tub or outside, not in the sink you just took apart.
- Clear the trap arm
Shine a light into the arm where it enters the wall. Reach in with the bottle brush. If it is packed with grease or hair beyond reach, feed a hand auger in from here.
- Check the washers
The tapered side of each washer faces into the joint. Replace any that are flattened, cracked or hard.
- Reassemble
Line the trap up so the pipes meet without strain, then tighten the nuts by hand plus about a quarter turn.
- Test
Fill the basin, pull the plug, and wipe each joint with dry tissue to spot a drip. Tighten slightly only where it drips.
04 /How do you clean a slow bathroom sink stopper and overflow?
A slow bathroom sink is most often a hair mat wound round the pop-up stopper, a few centimetres below the drain opening. Cleaning it takes a few minutes.
- Find the pivot rod
Behind the tailpiece, a horizontal rod enters the drain pipe, held by a small nut. It connects the lift handle to the stopper.
- Release the stopper
Unscrew the pivot nut, pull the rod back a little, and lift the stopper out from above.
- Clean it
Pull off the hair and slime, scrub with a toothbrush, and soak it in white vinegar if it has mineral crust.
- Clear the drain below
A barbed plastic strip pulls out hair still in the tailpiece.
- Reinstall
Drop the stopper in so the pivot rod passes through its loop, then retighten the pivot nut by hand.
Push-button stoppers usually unscrew from the top. Grid strainers that do not lift out need a barbed strip. A sour smell with a clean trap often comes from the overflow channel: scrub it with a bottle brush and a little dish soap, then rinse.
05 /How is a kitchen sink different?
Kitchen sinks clog with grease and food rather than hair, and they often have a disposal, a dishwasher and two bowls sharing one trap. Each of those adds a place for trouble.
- Double sinks: if water from one bowl rises in the other, the clog is past the tee, in the trap or trap arm.
- Disposals: switch off the power before reaching near one, and never put a hand inside. Fibrous food clogs the disposal outlet and its elbow; many units also have a socket underneath for freeing a jammed grinder with a hex key.
- Dishwasher will not drain after a new disposal: the knockout plug in the disposal's dishwasher inlet may not have been removed during installation.
- Dishwasher drain hose: it should rise in a high loop or go through an air gap on the counter so dirty sink water cannot flow back into the dishwasher. A clogged air gap cap can be pulled off and cleaned.
If a kitchen sink slows again within weeks of a trap cleaning, the grease is in the branch beyond the wall. The fix for that is covered in kitchen drain grease.
06 /What should you clean sink pipes with?
| Cleaner or tool | Use it for | Not for |
|---|---|---|
| Dish soap and hot tap water | Grease film on removed parts and near the opening | Clogs inside the wall |
| Bottle brush and old toothbrush | Traps, tailpieces, stoppers, overflow channels | Anything beyond the trap arm |
| White vinegar | Scale and soap scum on stoppers and strainers | Grease plugs |
| Baking soda | Deodorizing and mild scrubbing | Clogs |
| Hand auger | Clogs in the trap arm and branch | Disposals; forcing through a tight fitting |
| Chemical drain opener | Nothing: it makes the trap dangerous to open | Any sink you may need to take apart |
For what the popular home remedies actually do, see baking soda and vinegar for drains and bleach, peroxide and solvents in drains. For plastic trap materials and safe auger heads, see ABS and PVC pipe cleaning.
07 /When is the problem past the sink?
The problem is past the sink when a clean trap does not fix it. These signs point further down:
- The trap and arm are clean and the sink is still slow.
- Both sinks in a bathroom, or the sink and tub, are slow together.
- The sink gurgles when a toilet flushes or the washer drains; see main stack and vent cleaning.
- Water rises in a basement floor drain when the sink drains.
- The sink smells even with a clean trap and full water seal.
| Item | Typical range |
|---|---|
| Replacement plastic P-trap kit | $10 to $30 |
| Pack of slip-joint washers | $5 to $10 |
| Sink drain cleared by a professional | $150 to $350 |
Where a home fix ends and a professional call begins is set out in DIY vs professional pipe cleaning. If you need help, request quotes.
FAQQuestions people ask
How often should I clean the P-trap under my sink?
Only when the sink slows or smells, for most households. Bathroom stoppers benefit from a monthly clean in homes with long hair, and a kitchen trap in a heavy-cooking household may need attention a few times a year.
Can I clean a P-trap without removing it?
Partly. Some traps have a cleanout plug at the bottom, and a barbed strip or hand auger can work through the drain opening. Removing the trap is still the most thorough way.
Why does my sink smell even after cleaning the trap?
Check the overflow channel, which collects slime, and make sure the trap holds water. A persistent smell with a full, clean trap can point to a venting problem or a leak at the wall connection.
Why does the trap leak after I put it back together?
Usually a washer is missing, flipped, flattened or out of line, or the pipes meet at an angle. Loosen, realign, check the washer's tapered side faces the joint, and retighten by hand plus a small turn.
What is the best thing to clean sink pipes with?
A bottle brush, dish soap and hot water for parts you remove, and a hand auger for clogs past the trap. Avoid chemical drain openers in any sink you might need to take apart.
Should the trap arm slope?
Yes, a trap arm needs a slight downward slope toward the wall so water drains without siphoning the trap. A trap arm that runs uphill or sags collects debris.
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