Fuente: WIPO "rice" A run of an existing sewer (10) having at least one lateral sewer line (12,13) connected thereto is relined by applying an identifiable marking (14) to the wall of the existing sewer (10) or lateral (12,13), the marking being applied at a predetermined position relative to the mouth (15) by which the lateral is connected to the sewer, the marking being formed from a composition which includes magnetically detectable material. A liner (11) of plastics material is introduced into the run of the existing sewer, which liner overlies the mouth (15) of the lateral. The predetermined position of the marking (14) is magnetically detected with a detector 21, a cutter (22) is applied to the wall of the liner (11), following detection of the position of the marking (14), at a position which is in registry with the mouth (15) of the lateral, and the wall of the liner is then cut- through to communicate with the mouth of the lateral.