The term "sewer" as used herein shall mean any underground conduit composed of metal, concrete, clay, vitreous or other materials designed for the flowage of water or any waste product or products (including, without being limited to, storm sewers and sanitary sewers), and shall include any and all junction boxes, manholes and gutters and other appurtenances constituting any part of the sewer or of a sewer system.
The term "apparatus to detect the presence of any flammable gas or vapor", as used herein, shall mean any of the standard devices commercially available designed to detect, by the principle of the wheatstone bridge or other recognized technique, the presence in the atmosphere of flammable gas or vapor.