Fire up your smoker to 225°F (107°C)
Trim excess fat and silverskin off pork butt. Rinse and pat dry with a paper towel.
Apply a thin layer of yellow mustard to the pork
In a small bowl, combine the dry rub ingredients. Use a fork to crush any lumps that may form.
Season the pork butt generously with the dry rub, working into any folds of crevices in the meat. Cover all sides.
Once the smoker is at 225°F, place the pork butt on the grates fat-side up. Close the smoker door/lid, and smoke for 3 hours.
Combine the spritz ingredients in a food-safe spray bottle. Spritz pork every 30 minutes.
Once the meat's internal temperature hits 165°F (74°C), place the pork butt in the middle of a double sheet of aluminum foil. Bring up the edges of the foil slightly to create a boat-like shape. Pour the remaining spritz mixture over the pork butt, and then wrap the foil tightly around it.
Place the wrapped pork back in the smoker. Smoke until the internal temperature hits 200°F (93°C), about 2-3 hours.
Pull from the smoker. Leave in foil and allow to rest for 30 minutes.
Carefully unwrap the pork. Using meat claws or forks, shred the meat to serve.