flesh out, flush out

Flesh out and flush out are both correct English idioms.

Flesh out means to make something more substantial by “putting flesh” on it:

• The descriptions are too sketchy; the author needs to flesh them out with more detail.

Flush out means to drive a hidden person or animal into the open.

• The police surrounded the building and began a systematic search in order to flush out the robbery suspects.
• The spaniel flushed out a covey of quail.