Australian sinks do not have one universal drain size because the fixture opening, waste fitting, trap connection and sanitary pipe are separate measurements.
The NCC 2022 System 3 verification tables list basin fixture connections as DN 32 or DN 40 under different design conditions. Kitchen sink connections are listed as DN 40 within that method.
| Component | Published example | What the size describes |
|---|---|---|
| Bathroom basin fixture connection | DN 32 or DN 40 | Values within the cited NCC verification method, subject to its design conditions |
| Kitchen sink fixture connection | DN 40 | The sanitary connection within that method, not the visible basket opening |
| Kitchen basket waste | 90 mm on one current Oliveri model | The model-specific fitting through the sink opening |
| Waste or trap assembly | May carry more than one dimension | The product drawing must identify the inlet, outlet, thread and seal |
These figures can all be accurate because they describe different components. A 90 mm basket waste does not establish the downstream pipe size, so the figures are not contradictory.
Why doesn’t the measured diameter always match the label?
DN means nominal diameter. It identifies a standard pipe size, but it does not promise that every inside, outside or thread measurement equals that number.
The way plumbers identify pipe and fitting sizes accounts for the component, measurement point, thread and joint type. A ruler measurement alone cannot confirm compatibility.
How do you identify the correct replacement?
- Name the fixture: distinguish a bathroom basin from a kitchen sink or laundry trough.
- Name the component: identify whether you are matching the outlet, waste body, tailpiece, trap or fixed sanitary pipe.
- Find the model: record accessible model numbers and moulded markings without disconnecting the assembly.
- Read the drawing: use the current manufacturer specification to check dimensions, threads, seals, overflow details and joint type.
- Check certification: search the WaterMark Product Database when that product category requires WaterMark certification.
Do not force, tape, glue or improvise an adaptor between parts that almost fit. Imported, older and commercial fixtures may use arrangements that differ from current domestic examples.
When does a licensed plumber need to check it?
The QBCC regulated plumbing guidance says maintaining, repairing, replacing or removing a plumbing fitting or fixture is regulated minor work requiring a QBCC licensee.
You can photograph accessible parts, read markings and check product documents without disconnecting the trap or altering pipework. Stop using the fixture if the assembly leaks.
If the sink is slow, check whether the issue could be an accessible blockage in the sink trap rather than the nominal pipe size.
Repeated kitchen restrictions may instead involve grease building up beyond the trap. Avoid dismantling fixed or concealed drainage to investigate it.
For a leaking, incompatible or persistently slow assembly, Q Plumbing & Drains can provide a blocked sink assessment and explain the appropriate repair.