Hey, sorry I didn't post earlier, I was dealing with several ill animals.
Wash pigs basically like you would a rat, but be very careful not to get water in their eyes and ears. I typically use a plain kitten or puppy shampoo (no flea killer, or anything like that), use warm water (not too hot), and lather and rinse as quickly as possible.
Most pigs hate it, but it's not an overly traumatizing experience.
Pigs do "groom" themselves, but it's not very effective. They'll sit and lick their paws and behind their ears, etc, but it seems to be more of a calming type ritual than an actual attempt at cleaning.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry