In most cases, no — installing a grease trap under your kitchen sink in New Zealand is considered restricted drainlaying work, which means it must be carried out by (or under the supervision of) a licensed drainlayer. That said, there are some nuances worth understanding before you pick up a spanner, and knowing the rules can save you from costly mistakes or compliance headaches down the track.
What Is a Grease Trap and Why Is It Required?
A grease trap (sometimes called a grease interceptor) is a plumbing device that captures fats, oils, and grease (FOG) before they enter the wastewater system. Without one, FOG can solidify in pipes and cause serious blockages — both in your home and in the wider council network.
In New Zealand, local councils often require grease traps for commercial kitchens, food businesses, and sometimes residential properties with high cooking loads. Requirements vary significantly by region, so always check with your local council before purchasing any equipment.
Is Installing a Grease Trap Restricted Work?
Yes — connecting any fitting or device to the sanitary drainage system (the pipes that carry wastewater away from your home) is classified as restricted drainlaying work under the Plumbers, Gasfitters, and Drainlayers Act 2006. This work must be performed by a licensed drainlayer or a licensed plumber who holds the appropriate drainlaying licence.
This applies even if the grease trap itself sits under the sink and looks like a simple add-on — because it must be correctly connected into your existing drain pipework to function properly and comply with the NZ Building Code.
What About Schedule 1 Exemptions?
The Building Act 2004 includes Schedule 1 exemptions for minor work that doesn't require a building consent. However, these exemptions do not override the licensing requirements under the Plumbers, Gasfitters, and Drainlayers Act. Even exempt work on sanitary drainage must still be done by a licensed tradesperson. Always confirm with your local council if you're unsure.
What Can a Homeowner Do?
While you can't legally make the drainage connections yourself, there are things you can do to prepare:
- Research and purchase the grease trap unit that meets your council's specifications (size, flow rate, and material requirements vary).
- Clear the under-sink space and measure up so the tradesperson can work efficiently.
- Talk to your council about whether a grease trap is required, and what standard it must meet (many councils reference AS/NZS 1546 for on-site domestic wastewater treatment).
- Get quotes from licensed drainlayers — you can find qualified local professionals on tradedirectory.co.nz.
Choosing the Right Grease Trap
Grease traps come in a range of sizes and materials. For a domestic under-sink installation, a small passive (gravity-fed) grease trap is typically used. Key things to consider:
| Factor | What to Check |
|---|---|
| Capacity | Sized to your sink's flow rate (litres per minute) |
| Material | Stainless steel or high-grade plastic — check council preference |
| Access | Must have a removable lid for cleaning and inspection |
| Compliance | Should meet any council or BRANZ guidance |
| Maintenance | Needs regular cleaning — typically every 1–4 weeks for busy kitchens |
You can browse grease trap options at stores like Bunnings or Mitre 10, or through a plumbing merchant — but confirm the spec with your licensed tradesperson before buying.
Maintenance: What You Can Do Yourself
Once a grease trap is professionally installed, routine maintenance is something homeowners can handle:
- Remove and clean the trap regularly (frequency depends on usage).
- Dispose of collected grease in the rubbish bin — never back down the drain or in the garden.
- Inspect seals and baffles for wear.
- Keep a maintenance log if required by your council.
Neglecting maintenance is one of the most common causes of drain blockages and foul odours, so don't skip it.
Healthy Homes and Rental Properties
If you're a landlord, note that the Healthy Homes Standards focus primarily on heating, insulation, ventilation, moisture, and draught stopping — they don't specifically mandate grease traps. However, you are still required to maintain the property's drainage in good working order, so a blocked drain caused by grease build-up could become a compliance issue.
Safety Note
Working under a sink involves exposure to wastewater and potentially hazardous biological material. Always wear gloves when cleaning a grease trap, wash hands thoroughly afterwards, and ensure the area is well ventilated. If you notice any signs of drain damage, cracking, or persistent odours, contact a licensed tradesperson promptly — don't attempt to repair drainage pipework yourself.
When to Call a Professional
You should always engage a licensed drainlayer or plumber for:
- Initial installation and connection of the grease trap to your drainage system.
- Any modifications to existing drain pipework.
- Diagnosing persistent blockages or drainage problems.
- Ensuring the installation meets your council's requirements and the NZ Building Code (particularly clause G13 – Foul Water).
A licensed professional will also be able to certify the work, which is important if you ever sell your home or need to demonstrate compliance. Find a qualified local drainlayer through tradedirectory.co.nz.