A p trap gully is used to stop bad smells emanating from the underground drainage system into the air around a property.
It comes in two variations: one with a 90 degree outlet pipe and one with a 45 degree outlet pipe. The top of the gully must be attached to hopper, which collects rain and wastewater. Hoppers can be either rectangular or square in shape.
The outlet, whether 90 degree or 45 degree, is elevated so that incoming water can settle at the base of the gully. This is crucial to the operation of a p trap gully – the settled water stops the bad smells from rising back up and out of the drain, as the gases can’t get through the water to begin with.
However, because of their shape, these kinds of gully are difficult to clean with a drain rod. Therefore, it is advised to clear the hopper top of any excess leaves and use a plunger or jetting hose to clean out the trap when necessary.