It's certainly possible for your mini pig to use a litter box or go to the bathroom outside, just like a cat or dog. Before bringing home a new mini pig, it's important to have a plan for house training.

If you plan to litter train, it's extremely important to limit the space in which your little piggy has access.  Although they use the litter box by default if it's around, they may not be able to find it (or find it again) if you give them access to a lot of square footage.  Closing your piggy in the bathroom with a litter box (that contains pine pellets and never cat litter) is a great idea. You can go in and visit your piggy until he's extremely comfortable with you, and has a great grasp on litter training. At that point, you can provide him a bit more space...and so it goes until your piggy has full access to your house, or whatever amount of access you plan for him/her to have.