Pat the pork butt dry and trim the fat cap off to ensure that the seasoning adheres to the meat.
In a small bowl, make your pork butt rub by combining 4 parts kosher salt, 3 parts black pepper, 1 part paprika, 1 part garlic powder, 1 part onion powder, and 1 mustard powder.
Add the pork butt to a large bowl and generously season the pork butt on all sides, then place it in the fridge uncovered overnight.
Remove the pork butt from the fridge and preheat your pellet grill to 275 degrees F.
Once your pellet grill has reached the desired temperature, insert a drip pan into the center of the grill and place the pork butt on the grill grates right over it to cook.
After around 5-6 hours, thread the temperature probe through the grommet and insert it into the pork butt to check for doneness. Continue cooking, spritzing the pork butt every so often to keep it moist.
Cook the pork butt for a total of 8 hours or until probe tender. The final internal temperature of the pork butt should be around 200 degrees F.
Remove the pork butt from the grill, cover it with foil, and let it rest for an hour before pulling apart to enjoy.