Green’s Dictionary of Slang

wayside ditch n.

the vagina.

1890–1904		Farmer & Henley Sl. and Its Analogues IV 340/1: The female pudendum [...] wayside-fountain; wayside-ditch.
1896		Farmer Vocabula Amatoria (1966) 117: Évier, m. The female pudendum; ‘the way-side ditch.’.