Refer to Manufacturer's Engine Service Manual for flushing and filling instructions. If none are available: 1) Remove upper and lower plugs on lower unit gear case and completely drain the old oil. 2) Install fill tube into lower hole. We recommend using Star brite Lower Unit Quart Pump (#27400, Lube Tube (#28600) and Adaptor (#28401, #28402) for easy installation. 3) Slowly refill unit with new lubricant until fluid appears at the lip of the upper hole. 4) Replace the upper plug and tighten it securely. 5) Remove the fill tube from the lower hole and replace the lower plug. Tighten securely.