I am new to working on my Jeep and I did this yesterday. Take Chris' advice.
1. I used the Prestone kit. You install a T fitting in the Heater hose that goes to the top of the engine. It was simple to cut the hose and install the T fitting. This allows you to flush the system at the hose with a simple connection point. Just follow the directions. I read them three or four times to make sure I had it.
2. The kit comes with an L tube to press into the radiator fill. There are two ends. The shorter fatter end appears to be the end designed to be pressed into the radiator fill tube under the pressure cap. It was too wide to fit mine so I turned it around and pressed the smaller end of the longer side into the radiator fill tube. Worked well but the flushing fluid ended up only extending a few inches out from the tube so the flush ran down into the engine compartment along the back of the grill. A post and video link posted on this site suggested the flush would shoot out away from the car. My water pressure must be too low to get it to flow forcefully enough. http://www.jeepforum.com/forum/f11/rad-flush-kit-165642/
Next time I will find a tube/hose to attach to the L tube and get the flush away from the engine compartment. See Also: http://www.jeepforum.com/forum/f11/whats-best-way-flush-cooling-system-171554/
Note recommendation for re-filling while engine running.
3. The instructions did not say to release the engine block drains although I would have if I could find them with some confidence that what I identified were the correct drains. It is at the bottom of the system, there has to be some gunk in there.
4. In my system, someone had mixed incompatible fluids, I used the Prestone which is supposed to be compatible with other fluids to refill.
5. I thouuoght you had to actually remove the piece that you unscrew to open the petck. I now understand you merely unscrew it to open the petcock to allow the fluid to flow out. It is not removed. Seems stupid that they have the petcock oriented horizontally and aiming to the rear. If it was oriented downwards you could fit a hose on it to direct the fluid into a container.
6. Chris- I thought you were recommending removing the lower radiator line instead of opening the Petcock on the bottom of the radiator. Sounds good to me. I finally figured out I had to remove the entire front grill/trim in order to gain sufficient access to the radiator drain plug. At first I just removed the grill and then the passenger headlight housing but it was not enough to allow purchase on the drain. Is there a better plug to install? I saw where one poster used a sawzall to cut away part of the fiberglass around the area to give better access.
7. After too many hours I did not use the flush cleaner. Some here have suggested it is a waste of time anyway. The flushing water looked pretty good. Maybe next time.
8. Replace your Radiator Cap while you are at it.