Put 1 sliced onion in bottom of crockpot. Add pork roast, cloves, water and one more onion, sliced, on top. Cover and cook overnight or 8-12 hours on Low. Remove meats. Cut away bone and fat. Drain away most liquid from pot. Reserve in refrigerator. Cut meat into small pieces and put back into pot. Add chopped onion, barbecue sauce, salt and vinegar if too sweet. Add back fat-skimmed pork liquid as needed. Cover and cook additional 1-3 hours or High or 4-8 hours on Low. Stir 2-3 times and break up large meat chunks. Serve from crockpot onto large buns with dill pickle slices.