12 each normally closed by a cover plate not shown before renovation the sewer is normally cleaned by conventional means and is proved by drawing through it a proving section shown in fig1 at 13 subsequently a liner 14 is formed and fed through the sewer pipe 10 both the proving section 13 and the liner 14 are formed principally of a strip sold under the registered trade mark rib loc and shown in section at 15 in fig3 the strip being formed with a number of t section longitudinal ribs and shaped at its side edges for interlocking engagement of one side edge of a section of the strip with the opposite side edge of an adjacent section of the strip by means of a winding head machine of known type indicated at 16 in fig2 the strip 15 can be drawn from a roll 17 and wound to a helix of predetermined diameter the convolutions of the helix interlocking one with the next as shown in fig3 the form a cylindrical tubular body a solvent cement can be injected into the interlocking edge portions of the convolutions during the winding process for increased mechanical strength and water tightness the proving section 13 is made at any convenient location by winding a fairly short cylindrical tubular section in this manner and applying to its leading end a nose cone 18 the proving section is brought into a.