an insert is provided for insertion through an opening in the surface of a conduit , the insert comprising an insert body having find and second open ends defining an axis of ! low therebetween the insert further comprises a valve flap connected to the insert body . the valve clap is moveable between a closed position , in which it creates a closure , thereby preventing flow along said axis , and an open position in which the valve flap allows flow along the axis . the valve ( lap is arranged so that , when in the open position , it is substantially u - shaped in side cross - section and is oriented with respect to the insert body so that said u - shape articles over the axis of flow .