Season pork loin with the salt and pepper, beer and chipotle seasoning . Place seasoned pork in a slow cooker.
Set slow cooker to Low. Cover, and cook overnight or 8 to 10 hours. Drain the juices and shred the meat into strands. Return the meat to the slow cooker; pour the enchilada sauce, garlic, diced onion and taco seasoning in with the shredded meat and cook on Low another 4 to 8 hours.