Stock in smaller slow cookers: You can certainly make stock in smaller, 3 - quart slow cookers! (thekitchn.com)
I have a couple of those very small slow cookers that are great for warming things like hot fudge sauce. (mamato5blessings.com)
I have a pretty small slow cooker (it has a 3.5 L capacity) and this recipe goes right up to the very top and did boil over a teeny bit. (heynutritionlady.com)