A permanently lubricated film gasket for providing a fluid-tight seal between a corrugated pipe and a smooth annular section of an outer pipe or section when the corrugated pipe and the outer pipe or section are in a relative surrounded and surrounding relationship. A first portion of the gasket is shaped to fit within a groove or recess of the corrugated pipe. A second portion of the gasket extends from the first portion. The second portion is at least partially comprised of permanently lubricated film for facilitating in the connection of the pipes along a single direction.

A method of rotationally molding a large-diameter pipe fitting, the wall structure of which is characterized as having a generally smooth interior surface and an exterior surface that is defined by a plurality of axially-spaced circumferentially extending ribs which are monolithically formed and homogeneous with the smooth interior surface of the fitting. The fitting is seamless and modularly designed with integral coupling elements at each terminal end, and with a ribbed wall structure profile capable of withstanding the loads typically found in buried applications with watertight performance requirements, where such ribbed wall structure meets the following dimensions and dimensional ratios: Rib Sidewall Angle (95-105 degrees); Bottom/Top Rib Thickness Ratio (1.80-2.80); Pitch/Rib Height Ratio (1.50-1.95); Rib Height/Fitting Diameter Ratio (0.04-0.09); and Avg. Rib Thickness/Rib Height Ratio (0.28-0.40).