just eye ball it, I raised the trailer jack until the black rub rail was pretty level. What I did was put the exact same amount of oil that I sucked out back in...that way you don't have to worry about over filling. These engines are extremely difficult to remove all the oil....suck out as much as possible, then crank over each engine a few times to get oil from the head and oil pump into the sump, then suck some more!! When your all done, make sure you check the oil level once the boat has been in the water idling for 5-10 minutes.
