Green’s Dictionary of Slang

(US) a chef or washer-up.

1896		W.C. Gore Student Sl. in Cohen (1997) 7: k.m. Kitchen mechanic.
1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 44: k.m. i.e. kitchen-mechanic, a servant girl.
1913		Fr. Klaeber ‘A Word-List From Minnesota’ in DN IV:i 11: K.M. A ‘kitchen mechanic’; a maid.
1928		R. Fisher Walls Of Jericho 176: I don’t want to be a K.M. all my life.