Place bones in crockpot, along with any optional juices.
Add onion, celery, carrots.
Fill crockpot to almost the top with water.
Add apple cider vinegar and salt. Sprinkle with any preferred spices.
Put lid on crockpot and cook on low for 12 hours.
Allow to come to room temperature, strain off bones and vegetables. Store in glass jars in the refrigerator for up to a week.