A new type of plug incorporating a normally closed valve for draining oil from
an oil pan of a car engine, wherein the normally closed valve is incorporated in
a through hole provided as an oil draining path in a bolt type member fixed to
the oil pan, an oil draining dedicated jig is assembled to the plug so as to open
the normally closed valve in order to drain the oil contained in the oil pan by
sucking it with a negative pressure, a movable valve disc member installed in the
through hole is installed so that it is engaged with a valve seat provided near
the outer end part of the through hole by a coiled spring so as to form the normally
closed valve, and the tip end of the plug is made flush generally with the internal
surface of the oil pan so as to prevent any structure from projecting toward the inside.
