Green’s Dictionary of Slang

skin flute n.

the penis.

1941		implied in blow the skin flute
1975		T. Berger Sneaky People (1980) 143: ‘Hell fire,’ said he in irritation. ‘It’s too late for a toot on the skin flute. Lay off!’.
1983		R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: skin flute See fleshy flugelhom, bed flute.
1997		Mad mag. Nov. 20: Whaddaya play, skin flute or male organ?
2004		J. Ellroy ‘Hot-Prowl Rape-O’ in Destination: Morgue! (2004) 257: Yeah, he died of AIDS – but he was no skin-flute hootin’ tutti-frutti!
2016		Chicago Trib. 3 Jan. FICT/11: I’m tempted to say, the skin flute, but [etc].

In phrases

blow the skin flute (v.)

to fellate.

1941		G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
1965		Guild Dict. Homosexual Terms 42: skin flute, to blow the (v.): To fellate.

play the skin flute (v.) (also play a skin flute sonata)

1. to fellate.

1968		A. Protopopov Milla 116: ‘I’ve never." Dergi started to say.—And Alexei finished, ‘... played a skin flute. [...] I’ve never had a male blow me either, but I think you would be quite musically inclined’.
1972		R.A. Wilson Playboy’s Book of Forbidden Words.
1989		P. Munro Sl. U.
c.1990		‘Robin Peters’ Satisfy Me! n.p.: She played his skin flute hungrily, as if she couldn’t get enough of it.
2009		B. Taylor Based on the Movie n.p.: [J]ewelry [...] can make the difference between years of marital bliss or your wife playing a skin flute sonata on some dude from her office.
2012		J. Dicker Harry Quebert Affair (2015) 27: Cock sucking, blow jobs, giving head, playing the skin flute [...] America is a pecker paradise.
2021		J. Ellroy Widespread Panic 177: She plays mean skin flute.

2. to masturbate.

1972		R.A. Wilson Playboy’s Book of Forbidden Words.
1989		P. Munro Sl. U.