All drains and sewer pipes connected therewith shall be so constructed and installed as to be completely watertight to a point at least four feet (4') above the bottom of the inside of the main or lateral sewer to which connection is made and in such manner as to prevent sewage which may build up in said sewer to a height of four feet (4') above said bottom of said sewer tile at a point of connection from escaping from the sewer through any opening, joint or loose connection in any such service line or fixture connected therewith; provided, however, that basement floor drains and other basement drains having an intake at less than the required elevation may be installed if provided with an automatic valve to prevent backflow and a manually operated shutoff valve by means of which all flow in the service connection can be positively cut off. The risk of sewage escaping through the malfunctioning of any valve so installed or from any connection made or maintained contrary to the provisions of this section, or from any other cause, shall be on the property owner. (Ord. 207, 7-17-1961)