In the slow cooker, place the pork loin. Sprinkle with salt, pepper and onion powder and rub into the meat. Sprinkle garlic and brown sugar over top, then pour in the beer.
Cover crock pot and cook on low for 6-8 hours, or on high for 3-4 hours.
About 1 hour before finished, remove lid and shred meat with forks or tongs. Mix thoroughly into the juices that have accumulated in the slow cooker.
Cover and let cook additional 30 minutes to 1 hour.
Serve atop your favorite hamburger buns drizzled with BBQ sauce, if desired.