Abstract: A device is disclosed for preventing clogging of main sewer lines by containing a potential back-up at the source, namely, the toilet. The device comprises an expansible annular member or ring which is adapted for placement adjacent the discharge tube at the base of the toilet, and is provided with circumferentially-spaced hook-like members which extend upwardly into the discharge tube and are so designed and arranged as to shred or catch material which has been improperly disposed of in the toilet, and without interfering with the normal use of the toilet to eject waste.