*Access structures, used for inspection and maintenance of the underdrain perforated pipes may be a maintenance hole or vertical standpipe connected to the pipe. Couplings used for standpipe connections should be 45° to facilitate pipe access by push camera or cleaning equipment. | *Access structures, used for inspection and maintenance of the underdrain perforated pipes may be a maintenance hole or vertical standpipe connected to the pipe. Couplings used for standpipe connections should be 45° to facilitate pipe access by push camera or cleaning equipment. |