Green’s Dictionary of Slang

1. (orig. US) human internal systems, e.g. the excretory tract, the urinary system; the genitals.

1943		in W.C. Fields By Himself (1974) 475: Keep your plumbing warm on your trip East and return home soon and safely.
1959		D. Niland Big Smoke 118: [He] went inside only for meals and the functions of his plumbing.
1959		‘Paul Merchant’ ‘Sex Gang’ in Pulling a Train’ (2012) [ebook] You’re just a lousy lay, is all, or you got something screwed up in your plumbing.
1969		‘Iceberg Slim’ Pimp 96: A con ran a shiv into my plumbing.
1975		(con. 1900s) G. Swarthout Shootist 105: Such was the state of his plumbing, he had to wait three or four minutes to achieve flow.
1980		E. Shrake letter 29 July in Davis (ed) Permanent Wave 240: The instant the tequila hit the other garbage in my stomach I whirled and threw up [...] Anyhow, I have given the plumbing three days of rest again.
1988		H. Max Gay (S)language 32: Plumbing—male genitalia.
1995		D. Lodge Therapy (1996) 94: I managed to produce a spurt of jism [...] so I know the plumbing is technically sound, but my cock is quite sore.
2001		J. Stahl Plainclothes Naked (2002) 5: At least the old skeek didn’t discuss his plumbing.
2013		T. Black Ringer [ebook] n.p.: Big Stauner’s the man, alright. Wouldn’t mind a piece of that. He looks a handy man. . . wonder if he’d take a look at my plumbing?
2017		T. Spicer Good Girl Stripped Bare i: As I spin around, I feel the ‘let-down’ and breastmilk almost squirts in his face. It seems there’s nothing dodgy about my plumbing.

2. (US) a trumpet, trombone, or similar wind instrument.

1935		Vanity Fair (N.Y.) Nov. 71: plumbing: trumpet.
1941		Pic (N.Y.) 24 June 24: What Do You Know About Music? [...] 18. What instruments are sometimes referred to as ‘woodpile,’ ‘plumbing,’ ‘licorice stick,’ ‘88,’ ‘skins’?
1951		Cosmopolitan July 85: You with the plumbin’, what’s your name?
2000		(con. 1940s–60s) Décharné Straight from the Fridge Dad.

3. fillings in teeth.

1955

J. Thomas No Banners 117: The fillings in his teeth had been removed and replaced by unmistakable French ‘plumbing’ [OED].

4. (Aus.) the lungs.

1996

S. Maloney Brush-Off (1998) 81: You thrash about sucking in air and fill your plumbing with froth and foam until you choke.