I dont see why you'd have to use the plug?? When we drained my radiator we just un plugged the hose, then just let it all run out, then once this is done, shuv the hose in the top, and let the water run threw the radiator, then push the hose back on (once u feel its clean, and all the waters drained out again), mix the fluid up, put it into the radiator, turn the car on, and leave the cap off the top, and wait for the car to reach opperating temp (there abouts) and check that the water is still right up the top of the raditor. Put the cap back on, and your set to go...
hope this helps!