How to Safely Remove and Clean a Drain Trap Under Your Sink

Removing and cleaning the drain trap (also called a P-trap or U-bend) under your sink is one of the most satisfying DIY plumbing jobs a homeowner can tackle. It requires no special licences, takes around 20–30 minutes, and can fix slow drains or unpleasant smells without calling a tradesperson.

What Is a Drain Trap and Why Does It Block?

The drain trap is the curved section of pipe beneath your sink basin. It holds a small amount of water at all times, which creates a seal that stops sewer gases from entering your home — an important requirement under NZ Building Code clause G13 (foul water). Over time, the trap collects hair, soap scum, grease, food particles, and other debris, leading to slow drainage or blockages.

Tools and Materials You'll Need

• Bucket or large bowl
• Old towels or rags
• Rubber gloves
• Adjustable pliers or slip-joint pliers (channel-lock style)
• Old toothbrush or bottle brush
• Mild dish soap
• Replacement washers or a new trap (if the old one is cracked or corroded)

You can pick up replacement P-traps, washers, and slip-joint fittings at Bunnings, Mitre 10, or PlaceMakers. Most standard traps in NZ homes are 40 mm or 50 mm in diameter — check your existing pipe size before buying.

Step-by-Step: Removing the Drain Trap

1. Clear out the cabinet and prepare

Remove everything from under the sink. Place a bucket directly beneath the trap to catch the water that will spill out when you disconnect it. Lay old towels around the area to protect the cabinet floor.

2. Turn off the water (optional but recommended)

You don't need to turn off the water supply to remove the trap, but it's good practice to avoid accidentally turning on the tap mid-job. Simply leave the tap off while you work.

3. Loosen the slip-joint nuts

Most modern plastic P-traps use hand-tightened slip-joint nuts at each end of the curved section. Try loosening them by hand first — turn anti-clockwise. If they're stiff, use slip-joint pliers, but be gentle with plastic fittings to avoid cracking them. Older homes may have chrome metal traps, which may need more force.

4. Remove the trap

Once both nuts are loose, slide them back along the pipe and carefully pull the trap free. Tip the contents into your bucket — expect some unpleasant-smelling water and debris.

5. Inspect the washers

Check the rubber or plastic washers (also called gaskets) inside each slip-joint nut. If they're flattened, cracked, or brittle, replace them now. New washers are inexpensive and prevent leaks when you reassemble.

Cleaning the Trap

1. Take the trap to an outdoor tap or laundry tub.
2. Rinse out the bulk of the debris with running water.
3. Scrub the inside thoroughly with an old toothbrush or bottle brush and a little dish soap.
4. Rinse until the water runs clear and there's no odour.
5. While the trap is out, use a torch to look up into the drain tailpiece (the straight pipe coming down from the basin) and the waste pipe going into the wall. If you can see build-up, use a bottle brush or a drain snake to clear it.

Reassembling the Trap

1. Slide the slip-joint nuts back onto the pipes (make sure they're facing the right direction — threads outward).
2. Seat the washers correctly inside each nut.
3. Push the trap into position, aligning it with both the tailpiece and the wall waste pipe.
4. Hand-tighten both nuts firmly. Do not over-tighten plastic fittings — hand-tight plus a quarter turn with pliers is usually enough.
5. Run the tap for a minute and check carefully for any drips at the joints. Tighten slightly if needed.

Preventing Future Blockages

• Use a drain strainer over the plughole to catch hair and food scraps.
• Pour boiling water down the drain weekly to dissolve grease build-up.
• Avoid pouring cooking oils or fats down the sink — these solidify in the trap and pipes.
• A monthly flush with baking soda followed by white vinegar, then hot water, can help keep things clear naturally.

For guidance on healthy, well-maintained homes, Tenancy Services outlines drainage maintenance as part of the Healthy Homes Standards, which is useful context for rental property owners.

When to Call a Professional

While cleaning a trap is DIY-friendly, there are situations where you should call a licensed drainlayer or plumber registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB):

• The blockage is further down the line and a drain snake doesn't clear it.
• You notice cracked, corroded, or leaking pipes beyond the trap itself.
• There is a persistent sewer smell even after cleaning the trap — this may indicate a broken trap seal or a venting issue.
• Water is backing up in multiple fixtures at once (a sign of a main drain blockage).
• You're dealing with cast iron or lead pipework in an older home — these require specialist handling.

Any work that involves connecting to or modifying the drain, waste, and vent (DWV) system beyond simple trap replacement is restricted plumbing work under the Plumbers, Gasfitters and Drainlayers Act 2006 and must be carried out by a licensed tradesperson. You can find qualified local drain cleaners and plumbers on tradedirectory.co.nz.

Safety note: Wear rubber gloves throughout — drain water contains bacteria. If you use any chemical drain cleaners before attempting this job, flush thoroughly with water first and ventilate the area well, as residual chemicals can cause skin and eye burns.

Sources & Further Reading

• MBIE Building Performance – NZ Building Code
• Plumbers, Gasfitters and Drainlayers Board – Licensed tradespeople
• Tenancy Services – Healthy Homes Standards
• BRANZ – Home maintenance guidance
• WorkSafe NZ – Safe use of chemical products
• Bunnings – Plumbing supplies and fittings