mid-15c., "slops fed to pigs," from hog (n.) + wash (n.). Extended to "cheap liquor" (1712) then to "inferior writing" (1773).
Empty and pretentious talk; nonsense; baloney, bullshit: It's hogwash. There's no such thing/ Bradley is too soft, too fragile. Hogslop
[first form 1882+, second 1990s+; fr the house waste fed to hogs; the date of hogslop is probably earlier; hog-slosh in the same sense is found by the 1940s]