Yes, in most cases a Kiwi homeowner can replace a corroded sink basket strainer without hiring a plumber. It's classed as routine maintenance rather than restricted plumbing work under New Zealand regulations, so no licence is required — as long as you're only swapping the strainer assembly and not altering any pipework or making new connections to the water supply. That said, if you're uncomfortable working under the sink or the job turns out to be more complex than expected, a qualified plumber is always a safe call.
What Is a Sink Basket Strainer?
A basket strainer (sometimes called a sink waste fitting or plug fitting) sits in the drain hole of your kitchen or laundry sink. It catches food scraps and debris, and it seals the drain when you want to hold water. Over time, the chrome or stainless steel finish can corrode, the rubber seal can harden and leak, or the body can crack — all good reasons to replace it.
Is This Restricted Plumbing Work?
Under the Plumbers, Gasfitters and Drainlayers Act 2006, restricted sanitary plumbing work must be carried out by a licensed tradesperson. However, replacing a basket strainer — which involves disconnecting and reconnecting the waste trap below the sink rather than any pressurised water supply — is generally considered maintenance that a homeowner can do themselves. You are not connecting to the water supply, so it falls outside the restricted work definition.
If you're unsure, check with the PGDB or your local council. And if the job involves moving the drain outlet, altering waste pipework inside the wall, or anything beyond a straight swap, stop and call a licensed plumber.
Tools and Materials You'll Need
- New basket strainer (measure your sink drain hole first — most NZ sinks use a standard 89 mm opening, but check)
- Plumber's putty or silicone sealant (check the strainer manufacturer's recommendation)
- Adjustable spanner or slip-joint pliers
- Basket strainer wrench or large groove-joint pliers
- Bucket and old towels
- Screwdriver
- Utility knife or putty knife
Basket strainers are widely available at Bunnings, Mitre 10, and PlaceMakers. Choose a stainless steel body for longevity, especially in a kitchen environment.
Step-by-Step: Replacing the Basket Strainer
1. Clear Under the Sink and Turn Off the Water
Although you won't be touching the water supply, it's good practice to turn off the tap and place a bucket under the P-trap to catch any water.
2. Disconnect the P-Trap
Loosen the slip-joint nuts on the P-trap (the curved pipe below the strainer tailpiece) by hand or with pliers. Slide the trap away and let any water drain into your bucket.
3. Remove the Old Strainer
From below the sink, locate the locknut that holds the strainer body in place. Use a basket strainer wrench (or large pliers with a rag to protect the fitting) to unscrew the locknut anticlockwise. You may need a helper to hold the strainer body from above so it doesn't spin. Once the locknut is off, push the old strainer up and out through the sink hole.
4. Clean the Sink Opening
Scrape away all old putty, silicone, and corrosion from around the drain hole using a putty knife. The surface needs to be clean and dry for a good seal.
5. Fit the New Strainer
Roll a rope of plumber's putty (about the thickness of a pencil) and press it around the underside lip of the new strainer body — unless the manufacturer specifies silicone instead. Press the strainer firmly into the drain hole from above.
From below, slide on the rubber gasket, friction ring, and locknut in the order shown in the instructions. Hand-tighten the locknut, then use your wrench to snug it up — firm but not overtightened, or you risk cracking the sink or strainer body. Excess putty will squeeze out around the top; wipe it away cleanly.
6. Reconnect the P-Trap
Reattach the P-trap to the strainer tailpiece, hand-tightening the slip-joint nuts. Plastic nuts should not need tools; metal ones can be gently snugged with pliers.
7. Test for Leaks
Run water and check all joints carefully — both around the strainer flange at the top of the sink and at every trap connection below. Dry everything with a towel first so drips are easy to spot.
Common Mistakes to Avoid
| Mistake | Why It Matters |
|---|---|
| Overtightening the locknut | Can crack porcelain or composite sinks |
| Skipping the putty or gasket | Leads to leaks around the flange |
| Not cleaning the old sealant off | New seal won't bond properly |
| Reusing a worn P-trap | Old traps often leak once disturbed — consider replacing at the same time |
| Wrong size strainer | Measure the drain hole before buying |
When to Call a Professional
Call a licensed plumber if:
- The sink drain hole is damaged, cracked, or non-standard in size
- There is evidence of water damage, mould, or rot in the cabinet below
- The waste pipework is corroded, leaking at the wall, or needs rerouting
- You have a composite, stone, or undermount sink where overtightening could cause serious damage
- You're not confident working in a confined space under the sink
You can find qualified local plumbers on tradedirectory.co.nz.
A Note on Healthy Homes and Rental Properties
If you're a landlord, keeping sinks in good working order is part of your obligations under the Healthy Homes Standards. A leaking or corroded strainer that causes water damage or mould could put you in breach — so don't put this job off.
Master Plumbers
