If you want a complete flush, get yourself some adapter and do it from the hoses next to the waterpump, or from the upper or lower radiator hose. You don't need to pull the peacock to drain the radiator, pulling the lower radiator hose will also drain the coolant from the radiator. Eitherway, you'll have to get the car warm enough to have to thermostat open up or it'll not really finish the flush.
