idealy the boat should be level. To fill the reservoir, fill from the fill hole and when oil starts to come out the top, put the vent screw in. (it helps to have another person helping you) make sure you keep constant pressure (as soon as the oil appears by the vent, dont stop the pressure, equalize it so the oil is just at the vent screw) when the vent screw is in, quickly take out the bottle or hose you are using and quickly insert the fill screw. you will loose a little oil, but not enough to be worried about. make sure you tighten both screws so they dont come out in the water. Wipe off all the oil, so you dont pollute the water.