Why a gate on the drain? If he's setup a Herbie he wouldn't want to restrict flow. If he setup a beananimal he would only restrict flow on the main siphon. It seems a strange place to put it. How many drains does he have?
I think plumbing is my favorite part of this hobby. I've plumbed my tank 3 different times now. I may be looking at a fourth time but we'll see.
I'm interested to learn something new here perhaps.