Green’s Dictionary of Slang

1. the mouth.

1984

Partridge DSUE (8th edn) 569/2: mid-C.19–early 20.

2. (US) a toilet; occas. attrib.

1950		J. Weidman Price Is Right 338: If your New Haven-trained brain is still functioning, you can pour another little item into the hopper.
1974		G.V. Higgins Cogan’s Trade (1975) 19: They’d go round and look in the tanks of all the hoppers. Guys always used to stash pints in there.
1989		(con. 1964) P. Theroux My Secret Hist. (1990) 217: Some Africans [...] who refused to flush toilet paper down the hopper.
2001		‘Randy Everhard’ Tattoo of a Naked Lady 5: The ‘hopper shot’ [...] tossing softballs into toilet seats.
2001		S. King Dreamcatcher 115: What he cared about was getting Rick McCarthy off the hopper.