110mm Underground Drainage Roddable Back Inlet Bottle Gully With Square Grid (Pack of 10)Bottle Gullies are usually used externally alongside the house wall when introducing waste or rainwater pipes into a foul drain. They can also be used on Surface Water drains to collect rainwater from paved areas. You should always check with your local authority before connecting rainwater pipes into a foul drain unless this is an existing situation.The top section of any gully should be at least 150mm below the Damp Proof Course Level.The square top of this gully swivels, enabling it to be fitted flush to wall or paving slab regardless of which direction the gully outlet pipe faces.A Back Inlet gully allows new inlets to be connected into an existing drain run. The outlet of this fitting is lower than the inlet to ensure that the air seal is maintained and that there is no backflow.Bottle Gullies provide a trap that stops foul odours from the underground drainage system from escaping into the air