Cut ribs into sections to fit in the cooker, about 3-4 ribs per section. Arrange ribs in cooker; pour in enough boiling water to fill the crock pot half-way, then pour in the apple cider vinegar. Place a piece of foil over top of crock pot, then place lid over foil. Cook on high heat setting for 2-3 hours. Remove ribs from cooker and discard the vinegar-water mixture. Pour half of the barbecue sauce into crock pot; place ribs back in pot, then pour remainder of sauce over ribs. Place foil back on crock pot, then top with the lid. Cook 2-3 more hours on low heat setting.