Summarize the following:
On the morning of the day you want to roast the turkey or the night before, remove the brine from the refrigerator. Pour it into a 5USgal (19l) food-safe bucket or cooler. Mix in the ice water. Consider using a 5USgal (19l) drink cooler. These have good insulation and a drain spout for easy clean up. Take the turkey from the refrigerator and remove the innards. Discard the innards and the pop-up thermometer if your turkey has one. Put the turkey breast-side down in the brine-filled container. The turkey should be completely covered in brine. If it isn't, place a heavy plate or dish on the turkey to weigh it down. Cover the bucket and refrigerate the turkey while it brines. If you're using a cooler with a lid, screw the lid on and leave it in a cool place while the turkey brines. The cooler with the turkey and brine should keep the turkey at 38F (3C) or below. If you think the cooler isn't keeping the turkey cold enough, refrigerate it.
Mix the brine with 1 gallon (3.8l) ice water in a large container. Submerge the thawed turkey in the brine. Chill the turkey in the brine for 8 to 16 hours.