1kg of pork bones makes 1-2 litre of broth
Rinse bones with boiling water to remove residue of blood and bone sawdust. This gives a cleaner looking broth
Fill pot to cover bones and add 1-2Tbsp vinegar (I like to use apple cider vinegar). This helps to pull out all the goodies from the bones into your broth.
Boil on a very low heat, or in a slow cooker, for at least the whole day. Perhaps even 2 days if you can. (using a pressure cooker will speed up the process).
When you think it's ready, or you want to use the broth, decant it off from the bones into another pot, or an Agee jar and when cool, refrigerate. With the fat layer on top, this broth will last for weeks in the fridge. Bring it out and make a delicious and nutritious soup within minutes.
You can also separately save the meat that will by now have fallen off the bones and will be very soft. Add this to the soup when preparing.