Had another look at the drain plug closely and found the "nut" at the top of it just had to be loosened.Take the theromostat out, and take the bottom hose of the radiator and run a garden hose into the thermostat hole and radiator.
I spent the extra 1 or 2 dollars and alaways use distilled water when refilling.
Ive never had any trouble with air getting locked into a old GM car.
If you can find a radiator shop you may be able to get a new pet cock soldered in.
Glad your "OK" and found the plug.Had another look at the drain plug closely and found the "nut" at the top of it just had to be loosened.
I forgot to relieve pressure with the rad cap first--loosened the drain plug nut and it the coolant exploded out of there
enough to shoot the drain plug a good 10 feet away.
I never thought I could move that fast---I got my hands in some cold water fast and luckily no burns--but
skin is real sensitive.
I wish I would have read your post first about distilled water.
Got a good deal on some extended life coolant from Napa and good to go.
Feel better knowing there`s fresh coolant in there and saved myself some $$$ doing it myself.