Cleanouts on concealed piping, piping under a floor slab or piping in a crawl space of less than 36 inches (915 mm) in height, or piping in a plenum shall be extended through and shall terminate flush with the finished wall, floor or ground surface or shall be extended to the outside of the building. Cleanout plugs shall not be covered with cement, plaster or any other permanent finish material. Where it is necessary to conceal a cleanout or to terminate a cleanout in an area subject to vehicular traffic, the covering plate, access door or cleanout shall be of an approved type designed and installed for this purpose.