Abstract: A thermoplastic corrugated drainage tube comprising annular peaks and valleys and a plurality of drainage openings internally cut about the circumference of each valley, the openings in each valley aligned with the openings in successive valleys along helical lines described by said openings. The method of forming the drainage openings comprises placing a cutting tool in the interior of the tubing and rotating the tool while moving the tubing axially past the tool. The cutting tool comprises a body having a plurality of radially projecting cutters spaced equidistantly about the cutter body and means for rotating the tool.

Abstract: A thermoplastic corrugated drainage tube comprising annular peaks and valleys and a plurality of drainage openings internally cut about the circumference of each valley, the openings in each valley aligned with the openings in successive valleys along helical lines described by said openings. The method of forming the drainage openings comprises placing a cutting tool in the interior of the tubing and rotating the tool while moving the tubing axially past the tool. The cutting tool comprises a body having a plurality of radially projecting cutters spaced equidistantly about the cutter body and means for rotating the tool.