I've used a cassette toilet for one season and it has been great. I have never stopped at a dump station, I either have dumped it in an outhouse while camping or in my sewer cleanouts when home. My cassette is filled with RV antifreeze and so winterization is not a problem. As for grey water, I have a plastic trash container that doubles as a temporary bucket to drain the tank while camping:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27948602/gotomsg/27952751.cfm#27952751I've poured the grey water in the drain at the water fillup pump in the campground.
I like having these portable options in a truck camper because I never have to break camp in order to dump these tanks.
Hope this helps,
Mike