1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 20Get this manual
MAINTENANCE
Changing Engine Oil
Engine Oil Capacity US Quart (1.0 Liter)
Oil Draining Procedure
1Lock the outboard in the full tilt up position2Position outboard so the drain hole is facing downward3Remove drain plug and drain engine oil into an appropriate container4After the initial oil has been drained, temporarily reinstall the drain plugDisengage the tilt lock and lower the outboardWait minute to allow the remaining oil that was trapped in the engine to return to the drainReturn outboard to the full tilt position and drain the remaining oil5Lubricate the seal on the drain plug with oil and reinstall