An easier way is to open the petcocks on the block ( there should be 2 ) and let the block drain completely. Then, close the petcocks. Disconnect 2 of the water hoses ( 1 goes into the water pump ) and just pour your anti-freeze right into the block until it is full. I have 4 cylinder Ford block and if I recall correctly, it holds about 1 1/2 gallons of anti-freeze. That's better than just draining the block and leaving it. You will get some rust in there over the winter if you don't put the anti-freeze in. Also, if you have to leave your boat outside over the winter, you should leave the outdrive all the way down, so you don't get water/melted snow and then ice in there.