Green’s Dictionary of Slang

dip n.2

[ext. use of SE dip, to plunge in]

1. a bout of quick sexual intercourse.

[UK](con. WWII) G. Sire Deathmakers 198: I’d like to have a quick dip.
[Aus]D. Ireland Glass Canoe (1982) 188: Her sister was a cheap prostitute in the pub where she worked — you know, a quick dip upstairs, then minutes later she’d be down serving beer in the bar.

2. (US prison) one who participates in anal intercourse.

[US]P. Hamill Flesh and Blood (1978) 32: You are what is known as a white fuck. A white fuck don’t do easy time. You can be a duke or a dip, a fuck boy or a jailhouse punk.