The night before rub mustard over the pork and the rub in the rub mixture. Wrap in plastic wrap and refrigerate over night. The next day bring smoker to 225º add apple or hickory wood to the coals and place pork on top grill. (or in oven or grill set for indirect heat). Monitor heat and keep it around 225º until pork reaches 185º to 195º. This will take 1 1/2 to 2 hours per pound. Depending on the size of your butt this could take all day. About once an hour spray or mop your butt with the mop mixture. Remove pork and let cool for 30 minutes. Pull apart with fingers or forks and serve on soft buns with your favorite BBQ sauce and coleslaw.
For 'real' BBQ flavor this should be cooked in a BBQ smoker but if you don't have one this can easily be done in your oven or crock pot. You won't get the same slow smoked BBQ flavor but it will still be good. For the oven place you butt on a rack in you roasting pan, pour plenty of the mop in the bottom and cover. Roast at 250º until pork reaches 185º to 195º. (Check periodically you may need to add more liquid to the pan.) In the crock pot add 2 cups of mop and let it cook all day until it pulls apart easily. Be sure to drain any fat.