Place the pork tenderloin in the bottom of your crock pot. Poor the root beer over the meat and cover. Cook on low until well done and the meat shreds easily; about 6 or 7 hours. Drain the pork well and stir in the barbecue sauce, shredding the meat as you go. Serve on toasted kaiser rolls. Cole slaw is delicious on the side, or on top of the pulled pork.