FOR THE PULLED PORK
Cut the pork butt into medium (2 to 3 inch) chunks
Put the pieces in a large slow cooker. Sprinkle the meat with the rub, turning the pieces to coat evenly. Add the bottled liquid smoke.
Cover and cook on high for 5 to 6 hours or on low for 10 to 12 hours, until the meat is pull-apart tender and reaches an internal temperature of 190 F.
Using tongs and a slotted spoon, transfer the meat to a platter or baking sheet. Let rest until cool enough to handle. Pull the meat into strands (it should shred easily). Serve the barbecue piled on buns with your favorite barbecue sauce.
FOR THE DRY RUB
Combine all the ingredients in a jar with a tight-fitting lid. Shake to blend.
To serve the barbecue later, cover and refrigerate the meat when it has cooled. Pour the meat juice into a separate container and refrigerate. Before reheating the juice, skim and discard the congealed fat layer at the top.
To reheat the barbecue, place it in a saucepan moistened with some of the reserved juice. Gently heat the meat on medium-low, stirring occasionally.
While the meat warms, combine the barbecue sauce with some of the reserved meat juice in a saucepan. Heat through and serve with the barbecue.