I've gone over the edge....again.
Along with proper use of it's and its, and to and too, and 90s and 90's (ps very few actual uses for 90's), and do's and don'ts (of course do's = do is or do was NOT the plural of do which of course does not exist), we have the proper pronounciation and spelling of the idea to "fill out the outline of the idea" -- and that would be to "FLESH out" (put meat on the skeleton of) an idea.
Flush out of course is a proper term in particular reference to hunting dogs "flushing out" the prey from the bushes so that people with long guns and hunting packs can take clear aim in the sky or on the ground. (I'm seeing several Jane Austen scenes in my head as I write this.)
Or even "flush it out" in reference to "flushing out" the car transmission or the bathroom pipes.
or Flush DOWN the toilet -- as in "we flushed those ideas they were crap" or "we flushed thouse ideas once we fleshed them out and saw that they had no legs."
I'm just saying.