Just did mine this morning, so I might answer the quesrion. :basketcase: If the pet-cock is turning and nothing coming out it is probably plugged, or the "T" is separated from the valve and is just free spinning. Use a 9/16 wrench to remove the whole bet-cock to let it drain from the hole. Be careful that it is not hot and try to control the rate as with the open hole it will gush.
When you refill, keep checking the level as the engine warms and burp the hose going to the thermostat. When it has warmed up and all the air out of the coolant keep filling at a rate of 1 pint per minute until the top of the fluid level is 1-1/4 inches from the filler neck. When all is warmed up and running with the coolant moving with the thermostat open you should be fine.
Then go do a burnout :drive: