Wastewater from your kitchen, bathroom and laundry is piped to a gully trap before emptying into the sewer. A gully trap is a basin in the ground outside the building and is connected to the nearest building drain/sewer so that foul gases from the sewer do not come to the house. It also prevents the entry of cockroach and other insects from the sewer line to waste pipes carrying wastewater.
The top or surround is raised above ground level to prevent groundwater, surface water and other foreign matter entering the sewer.
Gully traps are not meant for rain water.
In periods of heavy rain, a sudden increase in water flowing into the sewer through gully traps can result in wastewater overflows elsewhere in the sewerage system. These excessive flows can also cause problems at the wastewater treatment plant due to system overloading.
What should my gully trap look like?
The Building Code requires that all gully traps have an overflow level of the gully dish no less than:
i) 25 mm above paved surfaces (e.g. concrete, asphalt etc.); or,
ii) 100 mm above unpaved surfaces (e.g. soil, grass).
To further minimise stormwater or groundwater inflow into the wastewater system all property owners must ensure that:
a) any paving surrounding the gully trap is graded to convey all surface water away from it
b) all waste pipe connections to the gully trap remain water tight
c) any downpipes that currently discharge into the gully trap are redirected to stormwater.