Green’s Dictionary of Slang

well n.

the vagina.

c.1706		Dutch Riddle 1/1: It justly may be stil’d a Well / [...] / In Depth no Mortal Man can tell.
1748		Spy on Mother Midnight I 23: I find you are inclined for a long Line to plum the Bottom of your Well, but [...] fix or seven Inches will do as well, as one that could reach betwixt this and Lambeth.

SE in slang uses

In phrases