Place the pork shoulder in the bowl of a slow cooker. Add about 1/4 cup of water to the bottom to help prevent sticking.
Cover and cook on Low for 7 to 8 hours or on High for 4 to 5 hours, until the pork is very tender and easily shreds with a fork.
Transfer the pork to a large bowl and shred using two forks. Discard any excess liquid left in the slow cooker.
Return the shredded pork to the slow cooker. Pour in the barbecue sauce and stir to fully coat the meat.
Cover and cook on Low for 25 to 30 minutes, or until everything is heated through.