A tundish drain is a plumbing fitting that receives discharge water through a visible air gap, then directs it to an approved drainage connection. It is commonly used for water-heater discharge and air-conditioning condensate.
How it works
A tundish has three main parts:
- a receiving funnel or opening that collects water from the discharge pipe
- a visible air gap that physically separates the discharge pipe from the drainage system
- an outlet that carries the water to the waste connection
Unlike an ordinary closed drain connection, the discharge pipe does not connect directly to the waste pipe. The separation helps reduce the risk of contamination travelling back from the drainage side, while the opening makes any discharge visible. This is one example of how an air gap helps prevent drinking-water backflow. A tundish is not necessarily a complete backflow-prevention device for every application.
Visible flow confirms that water is being released, but it does not show why the connected equipment is discharging. Where it serves a water heater, check when relief-valve dripping indicates a problem.
Common uses
A tundish may receive:
- temperature-, pressure- or expansion-related discharge from some water-heating systems
- condensate from air-conditioning equipment
- discharge from other building services designed to drain through an observable air gap
The drainage destination must be suitable for the equipment and installation. A tundish does not make an otherwise unsuitable waste connection compliant or allow incompatible discharges to be combined.
In NSW, the tundish, its location and its waste connection must comply with current requirements for the installation. It should remain accessible so the opening and any discharge can be inspected.
Never cap, block or bypass a tundish. Water-heater discharge may be hot or under pressure. Keep clear and do not alter the fitting or pipework yourself; contact our licensed hot water repair plumbers for assessment.