Place roast and 1 cup water in slow cooker. Cover and cook on HIGH for 3 hours or LOW for 5 hours.
Remove pork from slow cooker and discard water. When cool enough to handle, shred pork into bite-size pieces; discard any excess fat. Stir pork together with barbecue sauce.
Stir together coleslaw mix and dressing. Place 1/2 cup pork mixture on buns and top with 1/2 cup coleslaw. Serve immediately.