Amazing build... gave me more ideas on what to do. as for your drain plan if it's going to be "permanenet" or semi maybe set-up a soaker hose system and just flip the valve to auto water a certain area. or even hook it up as you need to instead of dragging a hose around to water everything.
Thats a great idea, I was actually thinking of something kind of like that but using drip lines....the only thing is it will probably take FOREVER to drain this thing doing it this way