What is the minimum pipe size for a kitchen sink waste?
Summary (TL;DR)
According to AS/NZS 3500.2, the minimum waste pipe size for a standard kitchen sink (single or double bowl, with or without a dishwasher connection) is DN 50.
Kitchen Sink Waste Sizing (AS/NZS 3500.2)
Kitchen sinks handle high volumes of water, food scraps, and fats. Sizing the waste pipe correctly is essential to prevent blockages and slow draining.
The DN 50 Standard
For decades, the standard minimum waste pipe size for a kitchen sink in Australia has been DN 50 (50mm nominal diameter). This applies whether it is a single bowl, a double bowl, or includes a dishwasher spigot.
Fixture Units
Under AS/NZS 3500.2, a kitchen sink is rated at 3 fixture units. A DN 50 waste pipe installed at a standard gradient of 2.5% (1 in 40) can handle up to 10 fixture units, meaning a single DN 50 branch drain can comfortably handle a kitchen sink and a dishwasher.
Maximum Length of Unvented Waste
Remember that if the DN 50 waste pipe connects to a vented main drain, it can run unvented for a maximum of 10 metres (measured from the main drain to the trap weir). If the kitchen island is further than 10m from the vented drain, you will need to install an air admittance valve (AAV) or run a vent pipe.
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