When ever I have to drill, make new threads into a case I dont feel like splitting...
PRESSUREISE THE CRANK CASE with air.... best way is to have somone blow air into the crank case (blocking all outlets) so it blows all the air out the drain plug hole while you do the needed work... this will keep most of the metal shavings out of the motor (as it blows them out).... then a quick rinse/flush with mineral spirits will clean things out nice....