Green’s Dictionary of Slang

(US campus) a chamberpot.

1775		Essex Institute Historical Collections XIII 187: 5 Mingos and a Bed pan [DA].
1795		Will of Charles Prentiss in Hall (1856) 322: To him who occupies my study, / I give for use of making toddy, / A bottle full of white-face Stingo, / Another, handy, called a mingo.
1856		B.H. Hall College Words (rev. edn) 322: mingo [...] this word was formely used to designate a chamber-pot.