The Tundish provides a clear viewing area to visibly see when an unvented system is discharging due to an error condition. The dry trap tundish prevents odours or gasses from entering the building and eliminates the need to install both a tundish and a dry trap. It operates visually under full-bore discharge or a few drips. The discharge pipe from expansion valves, temperature relief valves and combined temperature and pressure relief valves should pass through a tundish with an AUK3 air gap. The tundish must be located within the same room, as near as possible to the relief valve, since it is important that the discharge is clearly seen to warn of a possible problem within the system.