I blanched them in my smaller stock pot and then, rinsed clean, I put them in my larger one with 1.5 pounds of mirepoix (2 parts onions, one part each carrots and celery, in large dice) and a bouquet garni of parsley stems (I froze a leftover bunch in water, and added the lot), bay leaves and peppercorns, plus 1.5 gallons of cold water.
I brought this to a boil and down to a very slow simmer and let it sit for hours, and then poured it into deli containers (purchased, not leftover.) I think I was fairly ingenious about this: I took a quart deli container, and put it in the smaller stock pot. I put the cheesecloth lined strainer over the deli container, and used a saucepan as a ladle to pour the stock through the strainer into the container - any overflow neatly caught by the stockpot, to be returned to the big pot. I cooled these off in a cooler filled with ice and water.
I now have about 2 gallons of stock, some in quart containers and some in pint containers, and all golden and beautiful, and sitting in my freezer.
(I also have a pot of meat sauce - had to make dinner, too.)
I also have two pot roasts. I'm inching towards yomtov. Got pretty much all my guests in line now.