A normally close valve is composed of a valve disc member (20) movably housed in an oil drain through hole (14) of a bolt member (11) fixed to an oil pan (1) and a valve disc (21) of the valve disc member (20) engaged with a valve seat (12a) of the bolt member (11) by means of a spring (30). An adaptor (40) connected to an oil suction hose (463) is used to push the valve disc member (20) to open the normally close valve and to drain an oil under negative pressure, and an elongated, flexible tube (50) connected to the oil suction hose (463) is inserted into the pan (1) from the adaptor (40) through an opening of the valve disc member (20) to drain an oil remaining on a bottom of the oil pan (1).