Fuente: WIPO "rice" An existing sewer run (10) which extends generally horizontally and which has access to the ground surface via at least one upwardly extending manhole shaft (12) is relined by feeding a first pipe length (14) of plastics material into the sewer (10) via the manhole shaft (12), the first pipe length having a wall which is corrugated to permit of resilient deformation of the portions of the pipe length as they bend in order to pass from the manhole shaft to the sewer, and feeding a second pipe length (15) into the first pipe length (14), the second pipe length having a smooth external surface to permit of easy insertion of the second pipe length (15) into the first length (14), and having a smooth internal surface which forms a low friction sewage-conveying surface for the composite liner thereby formed in the existing sewer by the first and second pipe lengths.