I haven't had trouble with rinsing out the Nalgene so far. I'm pretty fastidious with my gear, so everything gets cleaned thoroughly shortly after I get home, which helps. Otherwise, while I'm out, if there's a water source nearby I just rinse with that (not dumping the leftovers into the water obviously), if there isn't, I'll pour about half a cup of my supply into the Nalgene and rinse, shake, and scrub thoroughly with my hands.

The older powder was a bit tougher to clean (but not difficult), the newer one is easier.

Mountain House probably got better since I last tried their stuff, but it still requires stopping, cooking, cleanup. I've got an MSR Windburner and I love it for what it is, but if I just want to put down a lot of miles for a quick trip the Soylent is king. I'm >this< close to being able to do a Summer overnight with my 12L BD Bbee.

...of course, developing some serious intestinal discomfort 18 miles from the car would suck, so there's that.