Those photos work, thanks.
The top is standard. At least that's what I've seen in all the ones I've looked at (a few in person, most in photos). Mine has a simple, neatly drilled hole in the bottom with a plug like I referenced.
I'm not where my darkroom is right now but, if I recall correctly, you can't access the inner side of that outer plexiglass due to the glued in inner wall. So any drain fitting would have to be glued in.