You just turn the intestines inside out - there are usually tears in them where you can make shorter lengths to make it easier. Have a bowl of clean water in the sink and deposit them in it. Take a length out and put it on the draining board. With the back of a knife or other smooth but not too sharp object, simply scrape off what is inside leaving a thin casing.If you have the cold tap running gently the stuff will go down the sink, or you can direct it into the bowl, but don't let the unscraped casings escape down the plug hole! At first you may tend to stop without scraping everything off, so do try scraping a bit harder until you end up with a thin skin. If you don't get it all off it won't hurt you, it will just make the sausages tough! Give them a final rinse and then pack in plenty of salt in a margarine carton or similar. Soak for a couple of hours before use.