drop the soap (in the shower), v. — Green’s Dictionary of Slang

drop the soap (in the shower) v.

[orig. gay use, but also as a semi-joc. warning from one self-proclaimedly heterosexual young man to another, I wouldn’t drop the soap while he was around]

to make oneself available for anal penetration.

1979		Maledicta III:2 231: He also may or may not know the following words and expressions: [...] bend over (Navy: drop the soap in the shower).
1993		M.B. ‘Chopper’ Read How to Shoot Friends 119: He used two to four $50 caps of heroin per day and so he was flat out dropping the soap in the shower to pay his way.
2021		A. Parks April Dead 32: ‘So how was [prison]?’ asked McCoy. ‘Didn’t drop your soap in the showers, did you?’.

In phrases

play drop the soap (v.) (also play pick up the soap)

(US) to indulge in homosexual activity; also attrib.

1953		L. Uris Battle Cry (1964) 135: I hear [...] he’s been playing drop the soap with Bryce.
1972		B. Rodgers Queens’ Vernacular 22: Out to sea, boredom is relieved by playing drop [pick up] the soap.
2005		M.B. ‘Chopper’ Read Chopper 4 92: The drop-the-soap competitions had been getting completely out of control.
2024		J. Meades Empty Wigs (t/s) 514: [W]e afterglowed in my emperor size bed [...] We’d played drop the soap for a good hour!