I used a variation of others techniques. I wiped their behinds while they were sitting in the litter box, then I covered it by scratching litter over it when they were done.
I never tried anything specific to teach them how to groom themselves. I washed them regularly, but I think they picked that up from the other cats in my household.
But a funny story about my orphans: 2 of the kittens from Muddy/Koko's orphaned litter were adopted to a friend of mine. My friend has a fenced back yard and she lets them outside (under supervision) when the weather is nice. She has 4 cats. The 2 orphans have to run inside to use the litter box in the event that they need to go. The other 2 will just dig in her gardens. Orphans can get really anal retentive (pun intended) about using a litter box.
