Indeed Fireman, so did I but there seemed to be a little confusion
Evan, you need to ensure that there is a double check valve protecting the outside tap, best practice dictates that it should be on the pipe inside, after the isolation valve. I'd check with whoever installed the tap to confirm the tap has backflow protection or take a picture of the outside tap and post it and you will be advised.
If you google draincock/tap, that should show you how to use them, though if you're not sure, I always recommend you get a professional to show you how to use it correctly. You don't drain the drain cock, you drain the pipework via the draincock