Actually, I think they were suggesting that it would drain more evenly if there were cross members on Ts or Xs going to the main drain line. I don't think it would make any difference moving the main drain line to the edge.
Assuming the mash liquor will start above the existing drain, I would just use that one with a weldless fitting. With a hose hanging down on the drain, the siphon will suck that thing dry, regardless of how high the exit port is in the cooler. Even if you just had a hose draped over the side, it would work too as long as you can start the siphon.