An improved marine drain valve is disclosed. The valve includes a valve barrel having an intake opening and a discharge opening. A fluid passageway extends between the openings. A valve adaptor body surrounds the valve barrel and a torsion-compression spring is positioned between and attached to the valve barrel and the adaptor body. A vent passageway is defined by the valve for venting a reservoir to which the valve is attached. An operating pin extends outwardly from the valve barrel and is received for movement in a configured slot defined by the adaptor body. The slot has a first leg parallel to the valve barrel and a second leg extending perpendicular to the first leg. The spring urges the valve toward a nonoperating or locked position. To operate the marine drain valve, a user rotates the operating pin and forces it upwardly into the first leg of the slot thereby opening the valve. Upon release, the spring returns the operating pin to the locked position.