Put bones in pot and pour water until it's covered by 3 inches extra. Add apple cider vinegar. Boil and simmer for 3 hours or longer.
Alternatively, follow these instructions but make it in a crockpot. Turn on high for about an hour and then turn to low for up to 20 hours.
Pour mixture through a strainer and into a container. You may choose to pick out any meat bits, but make sure you don’t include any sharp bones! Add parsley or oregano.