Okay, so I've tried the different suggestions I've read here and elsewhere. And I've been wondering...
ONE - Is that first rinse/soak in cold water only necessary if you *don't* flush/dunk/rinse poop off first?
I obsessively rinse all traces of poop off DD's dirty dipes before putting in the pail (well, it's a canvas laundry bag for me, the pail stunk too much). If there's a stain remaining, or if I've just done a washload of dipes and it will be a while before my next load, I spray a little Nature's Miracle on it too.
I also spray a little NM on hemp dipes if they are really wet, because of the stink factor.
I have noticed no real difference in the loads I've soaked first in cold, then washed on hot, and the ones I didn't, other than the time factor involved.
TWO - What is the reasoning behind vinegar in the rinse cycle?
I tried it, didn't notice a difference with that either, other than my PUL covers smelled like vinegar. (I have that bionic pregnant nose thing going on right now.)
THREE - Is that extra rinse at the end of the wash really necessary unless you are having signs of a buildup problem?
Yet again, I have not seen any real difference when I did or not, except on some used dipes I got in trade that definitely had a build-up problem.