Well, here's a couple of pics to show you one way of doing it.
Here you can see the "water knot" up top, just peaking out enough to grab. The 'biner is usually rigged on the PC until needed.
Here you can see how the line is threaded down through the back (it's actually woven into the molle webbing) and handle "S" folded up top. When fully deployed, the handle is long enough to support the head/neck, and allow two guys to drag. The 'biner attaches to the riggers belt, so you are pulling from the belt, not the PC.
What runningwolf wuz saying is that some guys are improving on this by adding a cobra buckle in here. Quite similar to the old school technique of sewing a delta around back, but for different purposes.
Note Canadian button pull tabs, which actually work quite well, especially in low light.