Somehow it seems that sausage and hotdog casings, being made of sheep intestine, would not be readily cleaned out. They have to be full of little polypy things to do the digestion, right? At least as rough as the rough surface of the tongue.
And they are long and twisty, and not cut into shorter lengths until after stuffed.
So if you just squirt water through them is that all? Is that enough?
I believe the franfurters you buy for $1/lb have no casing at all and it is just the protein which binds the outside together when it is precooked. The other ones which do have casing, I believe it is synthetic and not cat’s gut any more.
I think you’ll find that the casing is not the intestine per se (that would be chitterlings), but the membrane that surrounds the intestine.
After you read this link, you will never eat sausage with natural casings again. 
Official UN “how to make sausage” page, with diagrams.
http://www.fao.org/docrep/003/x6556e/X6556E03.htm
Note: It’s for small-scale, Third-World sausage-making, but after reading it, I somehow lost my appetite for finding out how Hormel and Armour make sausage.
As Fredrick the Great used to say, “Sausages and treaties should be made in secret.”
Are you thinking of Bismarck’s maxim that “People should not see how laws or sausages are made”? Unless he was himself paraphrasing ol’ Freddy (?).
From my childhood memories of killing and processing a pig, it wasn’t a big deal. My grandmother washed the casings in several changes of salt water and then stuffed the sausages.
Which were damned fine sausages. Paprika and garlic and pork. Then they smoked some of them for salami.
I’m hungry now.
The same way that porcupines make love.
Veeeeery carefully.
For your naturally cased cocktail franks, they use lamb casings. Sheep, pig and cow casings are used for larger Frankfurters, sausages or salamis.
It is a natural and wholesome method of containing ground meats for future processing.
Have you ever had a synthetically cased sausage?
Try eating a cheap garlic sausage sometime. You’ll be chewing on the fake casing for longer than you wish to think about it.
The ‘snap’ of a fine hot dog or Frankfurter is entirely dependent upon the membrane tension of the casing used.
Get over it.