The word “Hogwash” is not slang, nor is it a recent coinage.
Five hundred years ago it was the common term for the swill fed to swine.
And, curiously enough, the earliest instance of its use traced by the Oxford English Dictionary, dated about 1440, reads “They in the kechyn, for iape, pouryd on here hefd hoggyswasch” They in the kitchen, for jest, poured hogwash on her head).
Some joke! In figurative contemptuous usage the term dates to the early eighteenth century.