Lots of water. I use the Geo method about once a month on the road and maybe twice a season when I'm doing short trips. Odor in the coach is a ventilation issue. Turn of all vent fans when dumping. I had to replace the bathroom ceiling vent/fan and replaced it with a Fantastic fan that reverses. This helps keep odors down by pressurizing the bathroom and forcing air out the vent pipe.
I found that you can get a smell flushing if the vent fans are on with all the windows closed. You're sucking air through the tank vent and tank into the coach. Now if I can only get the DW to understand that...
Another vent issue I've read about is the black tank vent pipe getting loose and dropping into the tank. You can check this by going up and removing the cap and see the the pipe is still above the collar.