Oh...Ok sorry about the misinterpretation.
Drain plugs are usually at the bottom of the exhaust manifolds and there should be a petcock on the side of the block to drain that.
I usually remove the lower rad hose at the water pump and open the petcocks on the block and manifolds to drain all the water out.
Once that is done, I close the petcocks and replace the lower rad hose. then I take the upper rad hose from the "T" split on the thermostat and fill up the entire engine with coolant (Prestone) until it overflows on the top of the block at the thermostat housing.
I hope that helps?