Peel and slice potatoes and onion. Make layers in slow cooker or crockpot as such: Potatoes, onion, smoked sausage (wedges of cabbage and/or mushrooms are great in this, too). Pour cream of mushroom soup over this. Add 1/2 soup can of water. Turn crockpot on low for all day cooking (about 6 hours); slow cooker on medium for about 3 - 4 hours. NOTE: It's fine to put smoked sausage in frozen, too.