What is a gully trap?
A gully trap is an outdoor drainage fixture that receives wastewater from household pipes and directs it to the sewer, featuring a water seal that prevents odours and backflow while catching sediment.
Found at ground level outside most Perth homes, a gully trap is the junction point where internal waste pipes connect to the sewer line. It sits in a pit and contains a U-bend or S-bend water seal (the trap) that holds standing water. This water barrier stops sewer gases and rodents from coming back up through the drain system and acts as a barrier between the household waste system and the public sewer.
The gully trap also serves an overflow relief function. If the main sewer line backs up or becomes blocked downstream, the trap allows excess water to overflow safely into the yard rather than flooding back into the home's plumbing. This protective overflow prevents raw sewage from entering bathrooms, kitchens, and laundries during blockages or heavy flow events.
Over time, gully traps collect sediment, grease, and debris that settle in the base of the pit. This accumulation can reduce flow capacity and eventually cause blockages. Leaves, food scraps, soap buildup, and mineral deposits are common culprits. When a gully trap blocks, water pools around the pit or drains slowly from outdoor areas. In Perth's clay-heavy soils and during storm events, tree roots can also infiltrate the pit and trap connections.
Regular inspection and cleaning of the gully trap prevents blockages and keeps the overflow mechanism functioning. If your gully trap is slow to drain or overflowing, a plumber can clean it or identify whether the blockage sits deeper in the sewer line. Drain blockage specialists routinely clear trapped sediment and restore proper flow.