Same place as the front, they both draw from the same washer bottle. If you run out and pump the system dry it may take a couple of seconds to refill the tube that runs from under the hood all the way to the back of the car once you have refilled the bottle.
Good to know it's just like in the VUE. I prefer one resevoir feeding both locations.
We had a '92 Explorer that had seperate resevoirs. It was a pain because the rear resevoir always seemed to run out at the most inconvenient time.