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 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 upper plug and tighten securely. 5) Remove fill tube from lower hole and replace lower plug. Tighten securely.