If you're going to drill and add a valve why not drain it in place? For that matter you could just drain the kettle with an auto siphon.
I've never been bothered by a little heavy lifting but as you get older your body begins to remind you of all the crazy crap you did when younger. I'm 59 and still in pretty good physical condition since I've always worked out and still referee high school and college soccer. I have no trouble lifting a fermenter with 5+ gallons of liquid in it but why do it if there's a smarter easier way. I pump the wort from the kettle to the fermenters which are on a wheeled cart, then roll them to the swamp coolers and lift them in.
My advice is find a resonable way to chill and drain in place. Save the heavy lifting for jobs where you can't avoid it.