PLAN AHEAD: Please note that, if you're going to brine the pork (which I highly recommend), you'll need to do so the morning before (24 hours ahead).
Add the ice to the brine and carefully pour it over the meat -- I would do this step in the sink, if the container fits. Cover the container with the lid (if there is one), or plastic wrap. Either way, make sure the meat is completely submerged in the brine, and that it's sealed tightly. Place the container in the refrigerator and brine for about 24 hours.
When you're ready to remove the meat from the brine, preheat the oven to 225° F, and adjust a rack to the lower third.
Place the pan in the 225° F oven and slow roast the meat for about 2 1/2 hours per pound. When it's done the internal temperature should be about 190° F.
Add the pulled pork back to the pan and gently toss it with the pork juices and bits of the spice rub that are on the bottom of the pan.