When I do a breakdown of the kegs, the posts and poppets get boiled to kill any nasties. The dip tube get the brush treatment.
Just as an aside, I cleaned up 3 kegs that I got recently from the LHBS, which had a lot of kegs come in. One had a hard to identify blue liquid, one had a red liquid that smelled like red pop, and the third a yellow fluid that smelled like old Mountain Dew - and not in a good way. These kegs all got broken down, cleaned, posts boiled, and the o-rings replaced.