The extent of the training for all my cats has been…scoop up the kitten when they have just finished eating, and plop them in the litter box, Do this three or four times until they use it. Once they have used it once, most cats have the jist of the lesson. When you move to a new place, set up the litter box before letting cats out of cages. When you let them out, scoop them up and plop them in the litter box before they see or do anything else, including the food area. They figure it out really quick.
Wasn’t even gonna mention that I also use an automatic Littermaid litterbox, which works great so long as you use something like World’s Best (read: expensive) Cat Litter in them. As close to maintenance-free as you can get…
Letting cats go outside is why I no longer have cats. I noticed that dogs lasted longer, but I thought it was because I just wasn’t really a cat person.