Green’s Dictionary of Slang

gazoo n.

[var. on kazoo n.]

1. (also gazool) the anus.

[US]E. Torres After Hours 127: Dave was becoming a pain in the gazool.
[US]H. Rawson Dict. of Invective (1991) 224: When Senator Alan Simpson (Republican, Wyoming) told reporters just before a press conference by Ronald Reagan on March 19 1987, that ‘You’re asking him things because you know he’s off-balance and you’d like to stick it in his kazoo,’ the word was rendered by The Wall Street Journal as gazoo [R].
[UK]Roger’s Profanisaurus in Viz 87 Dec. n.p.: gazoo n. Arse; bum.

2. (also gazookus) the vagina.

[US]H. Selby Jr Demon (1979) 42: Right up the old gazoo, the moist and hungry gazookus.

In phrases

up the gazoo (also up the gazops)

(orig. US) full up, as much as one can handle, to excess.

[UK]F. Pollini Glover 107: Blokes, Blokes, up the goddamn gazoo and out, man.
[US]G.V. Higgins Digger’s Game (1981) 22: When you got airplanes up the gazoo, I’m gonna be a nice fellow to know.
[US](con. 1969) M. Herr Dispatches 39: And this was still months before Tet, ‘refugees up the gazops,’ a flood.
[US]H. Selby Jr Requiem for a Dream (1987) 31: I thought we had money up the gazoo.