Access the water pump by using a screwdriver to remove the ride plate. Use the wrench to remove the bolts on the water pump and lift the siphon bilge pump out to expose the impeller. If the impeller is nicked or extremely corroded and dirty, remove the bolt holding it in place and remove the impeller. Apply marine grease to the new impeller and set it in place. Tighten the impeller nut, replace the bilge siphon pump and replace the water pump bolts. Also reinstall the lift plate with the screwdriver.