I keep hearing speakers use 2 different phrases: flesh out and flush out. I thought that flush out was not a thing at all. Looked it up; I was wrong. M-W says: Think of fleshing out a skeleton. To flesh out something is to give it substance, or to make it fuller or more nearly complete.

To flush out something is to cause it to leave a hiding place, e.g., "The birds were flushed out of the tree." It can also be used figuratively, as in "flush out the truth."

You're welcome. I knew you were dying to flush out the difference.