Abstract: Disclosed is a lubricant drain plug system for a casing of moving mechanical parts in lubricant. The system comprises an adapter plug body, an oil drainage assembly threadably mountable to the adapter plug body, the assembly having an outer plug with port holes, and a valve mechanism on the adapter plug body, the valve mechanism being positionable in either an on or off position. In use, the system is inserted into the casing so that the port holes are in the lubricant and the valve is positioned in the on position so that lubricant can flow from the casing out of the system. When the valve is off, lubricant flow is stopped.