The machine employs a forming collar to shape a continuous web of material longitudinally about a barrel with the longitudinal edges splayed outwardly and over each other. A sewing machine spaced radially from the barrel secures the longitudinal edges together to form a sleeve having an outwardly directed flap. In another embodiment, the machine employs two forming collars to shape a pair of webs about the barrel with outwardly splayed edges on two sides and two sewing machines to secure the edges together to form a pair of flaps. The seam(s) can be sewn at one of a plurality of spacings from the barrel to form a drainage line element of a different diameter from a standard diameter without need to adjust or replace other components of the fabricating machine.