Place the pork tenderloin in a slow cooker; pour the root beer over the meat. Cover and cook on low until well cooked and the pork shreds easily, 6 to 7 hours. Note: the actual length of time may vary according to individual slow cooker. Drain well. Stir in barbecue sauce. Serve over hamburger buns. After emptying crockpot, put a sheet offfabric softener in the pot wih HOT WATER and let it sit for an hour or so--the stuck-on food will come right off!