Positive pressure is used to induce the flow of a liquid lubricant from a crankcase and through a drain conduit so that used oil can be removed from the engine and collected in a container during an oil change procedure. Positive pressure is introduced into the crankcase, and into an ullage region above the liquid lubricant, by the use of an inlet valve that can be attached to a cam cover to replace a PCV valve temporarily during the oil change.