Hello--I've attached a photo of the watering system I use, which I've evolved from a method employed by Charles Ledgerwood, a seed purveyor in Carlsbad, Calif. until his death a few years back. He described himself as a "retired Rainbird installer for the city", and that his system was the exact opposite of the high-pressure method; he used PVC pipes as 'tanks', with leak-holes drilled in them.
His rows were watered with straight pipes connected with a manifold at one end. I believe they were glued together, but maybe not. In any case at one point I started simply pushing the pieces together, which works fine since there's virtually no pressure.
From there it turned out to be convenient to turn corners using angles--after awhile the squares evolved, naturally. I don't know a lot about the square foot gardening system other than how useful it is to divide a plot up that way, but it seems obvious to me that this method of watering could facilitate the technique.