Honda BF20A-BF25A, BF25D-BF30D Outboard Motors Shop Manual., Page 47Get this manual
HONDA BF80ASSA
3GEAR OIL
1) Position the outboard motor vertically2Remove the oil level plug and the oil drain plug and allow the gear oil thoroughly drain into suitable containerIf there is water in the oil, the water will flow out first when the oil drain plug is removed, or the oil will be milky colorIf water is detected, check the oil level and oil drain plug gaskets, gear case gaskets, and gear case sealsAlso check the toraue on the gear case bolts
OIL LEVEL PLUG
OIL DRAIN
3) Remove all metal particles from the magnet end of the oil drain
plug4) Use commercially available oil pump or squeeze tube to fill the gear case with the recommended gear oilPump or squeeze fresh oil through the OIL DRAIN plug hole until oil begins flowing out through the OIL LEVEL plug holeUse new sealing washers and install the oil level plug first and then the oil drain plugTighten the specified torqueTORQUE: 3.5 Gear oil capacity