Oil change/coolant replacement after Head gasket blowout

I am going to be installing new head gaskets this week. Since both the oil and coolant are contaminated, how do you get rid of the bad oil and coolant. I have already emptied both the oil and coolant. Do you refill both and run for a while (how long?) and then change it all over again. Is there any way to drain all of the coolant in the block? Do you run straight water for the first warmup and cool down?