Drain the oil? Why? Unless you left your oil fill cap off and submerged the engine, there's no reason that you should get dangerous amounts of water in your oil. I've rebuilt tons of flood cars, and draining the oil is NOT the first step in diagnosis.
When you hydrolock an engine, it's because water gets in the cylinders. Water, unlike air, cannot be compressed; thus, when your cylinders fill up with water (once it's sucked up through your intake, past the valves, and into the cylinders) your pistons can't compress it, so things start bending and breaking - most commonly connecting rods.
1. Remove the spark plugs, look and see if you can see any water in the cylinders.
2. Turn the engine over by hand. If you can turn it over, it isn't locked up.
3. Using the starter, crank the engine. Be sure and pull the fuse for the fuel pump and unplug the distributor first. If there's any water in the cylinders, and you didn't hydrolock it and/or bend a rod (or break something), it'll spin over and spit the water out of the spark plug holes.
4. Spray brake clean (flammable type ONLY) into the cylinders - not a shitload, but enough to mix with any moisture that may be in there. Hit it with an air nozzle and blow out whatever's left (be sure to not have your face directly over the spark plug hole while you're doing this).
I don't have a clue why you'd start out by draining your oil. Waste of time and possibly good oil, IMO.
Now, something else that I should mention, it's possible you didn't hydrolock it at all. When you get water on your air filter, it restricts the flow of the intake - and it CAN cause the engine to bog down and die WITHOUT causing any damage to anything. This happened to me waaaaay back in the day when I had my EG with a cold air intake on it. Same thing happens when you clean and oil your air filter, and don't wait for it to dry all the way before installing it and cranking your car - it just causes the engine to bog down.