Mine is drilled in the bottom. Bought it from an LFS that had a few extra after setting up shop. Wouldn't recommend it though, unless you're going barebottom, as obviously it is impossible to get to the bulkhead once you have sand and rock in the tank. This isn't necessarily a problem if you plan ahead and silicone in a drain pipe that you know will work, but it could be a problem otherwise.
Cheers,
Marty