All the boats I've owned had to have the oil changed with the dip stick tube and seems like being one quart shy is the case using this method.The tube can not go all the way to the bottom of the pan. Don't forget the oil filter has oil in it also.I have 2005 280 with twin 5.0's. I can only get 3 quarts of oil out of each engine when changing the oil. I'm using a dipstick style hand pump while the boat is on the water in the boat slip. Doesn't seem normal to me but wanted to check with others.