Tunneling for sewers is permissible in yards, courts, or driveways of any building site. When a pipe is driven, the drive pipe shall be at least one pipe size larger than the pipe that is to be laid. At the discretion of the city inspector, all excavations required to be made for the installation of a drainage system or house sewer, or any part thereof, shall be open trench work. All trenches and tunnels shall be kept open until the piping has been inspected, tested, and approved by the director of public services.
('69 Code, § 20-87)