You don't put drains in the block for flushing, you put them in there to DRAIN the block. You know, get all the coolant/water out of the block. So you don't drool coolant all over the place when you pull a head or something similar. Pretty sure the Prestone flushing kit doesn't get the sediment at the bottom of the water jackets out either. Since I've seen it come out my drains after a flush, draining all the water out for a proper refill.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
