If you used a 3/4 deep socket, you probably unscrewed the entire drain cock assembly from the block. All you need to do is use a 13mm open end on the hex that is a bit further away from the block than the big one one you put your socket on. This opens the internal valve and the coolant dribbles out. A piece of hose over the end avoids a mess and directs the coolant away from the exhaust pipes and into your container for proper disposal.

I have NEVER, on any car I can remember, been able to get all the coolant in there that they specify the system holds! And I've tried everything to drain heaters and hoses completely. After a few miles of driving, and cooled down a little, bleed off some coolant from the block drain, and test its anti-freeze properties. (You can take a cupful to a garage). Then you are assured about the freeze protection in the system. I suggest this method, cause lots of folks fill up the reservoir with pure water, or pure antifreeze, so there's no point in testing its contents, unless you have run the engine through about 5 dozen hot/cold cycles.
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar MGB, and numerous old motorcycles)