The connection of the building sanitary sewer into the public sewer shall be made at the "Y" branch, if such branch is available at a suitable location. If the public sewer is 12 inches in diameter or less, and no properly located "Y" branch is available, a neat hole may be cut into the public sewer to receive the building sewer, with entry in the downstream direction at an angle of approximately 45 degrees. A 45 degree ell may be used to make such connection with the spigot and inner surface of the public sewer. The invert of the building sewer at the point of connection shall be at the same or at a higher elevation than the invert of the public sewer. A smooth neat joint shall be made, and the connection made secure and watertight by encasement in concrete. Special fittings may be used for the connection only when approved by the Superintendent.