On the advice of others here on Sailnet (thanks, SD), I tapped the head sink drain into the head intake line so that the fresh water from the sink drain (i.e. after washing your hands) is used to flush the head. A diverter valve, a T-fitting and a bit of hose did the trick. It's a very simple solution to a stinky problem. Here's a diagram:
EDIT: Just re-read your post and noticed you're going to be living aboard, so this solution may or may not be workable for you.