Chris, for a year I have had the 320P (p for piston) which has been discontinued, but is closest to the 345. The 345 has these (relative) advantages over the 335: .8 taller, 1.5 wider, 1.8 deeper, (i.e., closer to a home toilet in size) 1.4 gallons more fresh water capacity, .6 more waste capacity, @6 more flushes.The biggest advantage to me was the bigger footprint. If you have the space for this one, I would recommend it. I also have an exercise step that I put it on top of (in the doorway) at night to make it even higher. My ancient knees find that much easier.