Most folks will say that, yes, you need to decant between each step. My starters are typically 2 or 3 steps and I always add the wort for step 2 right on top of step 1 once it has finished and only decant between steps 2 and 3, and if I have time, another decant before pitching. If I don't have time, I'll pitch the whole thing. I also always save a little off from the starter into a sanitized mason jar for a future starter.
a newB question but, I presume you're doing it for harvested yeast (maybe more step), washed yeast and Whitlabe/Wyeast whent there is not enough yeast for a high gravity beer?
When do you just do a one step starter. For exemple a 2liter starter without stepping it? With all the reading I do, I can only see when you use Whitelab/Wyeast and you have a "regular" OG beer. Am I right? I cant do one step with harvested or washed yeast?
Thanks!