Every establishment shall provide at least one public toilet room located on or near the premises for its patrons. Any toilet room installed on or after July 1, 1992, shall be not less than 18 square feet in area. The entrance to the room shall be effectively screened so that no toilet compartment is visible from any workroom. The room shall be kept in a clean condition and in good repair, well lighted and ventilated to the outside air, and effectively screened against insects and free from rodents. The floor shall be of concrete, tile laid in cement, vitrified brick, or other nonabsorbent material. All sewer drains shall be connected to an approved disposal system, and shall be properly trapped. No restroom shall be used for storage.