flush it vs flunk

flush it is not a noun while flunk is a noun.

Word	Noun	Adjective	Verb	Adverb
flush it	No	No	Yes	No
flunk	Yes	No	Yes	No

As verbs, flush it and flunk are synonyms defined as:

Other synonyms of flush it include bomb, fail.

flush it (noun)	flunk (noun)
	failure to reach a minimum required performance

flush it (verb)	flunk (verb)
fail to get a passing grade	fail to get a passing grade