Place chopped onion in the bottom of the slow cooker
Mix dry rub ingredients; coat pork evenly
Place pork fat side up on onions; optionally add water/broth around it
Slow cook LOW 8–10 hrs or HIGH 5–6 hrs until pork reaches 195–205°F
Rest 10–15 min; shred with forks
Optional: mix in slow cooker juices for extra flavor
