manhole, n. — Green’s Dictionary of Slang

manhole n.

1. in sexual contexts both based on hole n.¹ (1)

(a) the vagina.

1890–1904

(b) (US gay) the anus.

1972		B. Rodgers Queens’ Vernacular.
2001		Billy Bob ‘A Few Good Men 17’ on Nifty Erotic Stories Archive 🌐 I began by coaxing his sphincter open so that I could eat his assflesh deeper and deeper. Before long, the man was on his haunches and grinding his hairy fuckin’ manhole on my face. With my tongue I was able to open his butthole more and more.

2. (US black) a bar, a saloon, a club etc, esp. for men only [hole n.¹ (2b)].

1942		D. Burley N.Y. Amsterdam Star-News 21 Feb. 16: The Little Grey Hen’s been covering the ‘manholes’ these past few dims.
1983		R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].
1989		Kirk & Madsen After The Ball 364: Not having to stand in the Man-Hole for five hours every Saturday night.

manhole cover (n.)

(Aus./US) a sanitary towel; thus pl. manhole covers, menstruation.

1972		B. Rodgers Queens’ Vernacular.
1980		Maledicta IV:2 (Winter) 182: Most of these ‘functional’ terms are less succinct than the ‘hole’ terms and the last occurs also in the use of gentleman’s pleasure garden padlock for an S.T. (= sanitary towel) which is also known as a manhole cover or jamrag.
1999		J. Randall ‘A Visit from Aunt Rose’ in Verbatim XXV:1 Winter 26: Pads or tampons [...] have their own euphemisms: mouse mattresses, the white horse, manhole cover, coyote sandwich, saddle blankets, teddy bears, and the industry-sanctioned [...] feminine supplies.
2001		(con. late 1940s) Violet Foot Sixteen Shillings And Tuppence Ha’penny 133: Me darlin’ wife has either got a ’eadache tonight or she’s got her manhole covers (periods) – blow me down.