slosh (n.)

1814, "slush, sludge, a watery mess," probably a blend of slush and slop (n.1) in its Middle English sense of "muddy place."

slosh (v.)

"to splash about in mud or wet," 1844, from slosh (n.). Meaning "to pour carelessly" is recorded from 1875. Related: Sloshed; sloshing.