Fuente: WIPO "rice" A sewer (1) is relined by introducing a flexible tubular waterproof membrane (4) and then inserting a pipe or pipe length (5)(5a)(5b) into the tubular membrane (4). Grout (10) is then introduced between the sewer (1) and the membrane (4). A further membrane (7) may be provided so that the grout (10) is located between the two membranes (4,7). In the case where the sewer (1) includes an opening for a lateral connection (11), the grout (10) extending across the opening can be removed. Alternatively the grout (10) can be prevented from extending across the opening. Another tubular membrane (8) may be located within the pipe lengths (5)(5a)(5b) to be filled with water during the introduction of the grout.