What I did was put the shank in the oven on a cookie sheet at 350 degrees until it was brown. I rinsed the bones off and put them in the crockpot. When the shank was brown I added it to the crockpot.
I then put in some scraps of onions peals, celery and carrots that I had froze for stock. I poured about 1/4 cup of Apple Cider Vinegar on the bones and shank and let it sit for about an hour.