4. Accessibility to any valve, vacuum relief valve, back-siphonage preventer or vacuum breaker, backflow preventer, expansion joint, floor drain, sump, interceptor, flush valve or flush tank, water heater, hot water tank or cleanout shall be maintained. Should a construction or permanent obstacle be installed, a trapdoor shall allow access for maintenance or repair of that device. This also applies to the supply or waste connections of a lavatory, sink or laundry tray.