Trim all visible fat from the pork.
Place the pork in the bottom of the crock pot.
Poor root beer over until the meat is completely covered.
Add the sliced onion on top (optional).
Cover and cook on low until well cooked and the
pork shreds easily, about 6 to 7 hours.
When the meat is cooked through and it falls apart, drain most of the root beer. (I leave about 1/3 of the liquid to keep the pork moist).
Using two forks, shred the pork into bite size pieces.
Stir in the barbecue sauce and keep warm.
Serve on hamburger buns (optional) with sliced pickles, onions, and extra barbecue sauce.