laminarman:
The right way to do it is to first slosh it out with water and some soap, drain, then put in water and amonia mix at about one gallon per 100 gallons. Slosh it around, spray a little through the nozzles/pump; let sit 6 hrs (or overnight). Then for round up they recommend a product called nurtosol that neutralizes the acids in the roundup (you can skip this for most 24D or Milestone or Clopyd). You can then run either diesel through it or the rv winterizer.
Now that is what the "textbook" approach states. I personally just do the water soap slosh, drian, amonia water mix, let it set over night, rince it one more time with water, and then drain the hoses etc with air (or if I am going to use it in a month or so when it won't freeze don't drain). I then run a little diesel in the pump (just turn it by hand, dump some in the inlet).
This should work...