Flush out your casings and let them soak before you start any other prep with your sausage. If you use a normal cereal bowl size container about half full of water, add about ½ tsp. of vinegar to it (or in my world of wacky measurement, a drizzlebit or two.. lol!). This will soften them up but not too much (you'll get blowouts). Don't worry if you do a little too much, you can drain them, squeeze the water out and re-salt them and re-store them in the fridge again. Never freeze casings. Salted, they're good for a year or more.
Some casings are tougher than others, esp. the imported ones from China; I've not had good luck with those. I use casings from Syracuse Casing Co. from NY; they're domestic casings and are consistent quality and diameter; they don't need turning 'inside-out' and some sizes are pre-loaded onto plastic strips so they load onto your horn quickly and easily - you soak those like you do any others too. These are what are used in most meatrooms also. Their link is:http://www.makincasing.com/mm5/merch...ategory_Code=2
Their pricing is competitive and they don't charge shipping last I knew!