I just thought of another tip for making bone broth. When you're collecting your bones, put them in a big ziploc bag inside the liner pot of your pressure cooker (if that's what your going to use). Mash them down to fit the shape of the pot and put it in the freezer overnight. Take the pot out in the morning, but leave the bag as your "collecting bag" for bones. Or onions ends, whatever.
When you take the bag out to use the bones, it already fits your pot. That's helpful for getting as many bones in there as you can, and the more bones, the better the broth.