Green’s Dictionary of Slang

whiz n.⁶

an act of urination.

1967–8		Baker et al. CUSS 221: Whiz, take a Urinate.
1976		P. Conroy Great Santini (1977) 62: Your kidneys are gonna blow up soon, if you don’t take a whizz pretty soon.
1981		(con. 1966) P. Conroy Lords of Discipline 15: I never want to see you in the same latrine as me when I go to take a whizz.
1983		S. King Christine 106: I gotta go take a whiz.
1993		M. Myers et al. Wayne’s World II [film script] It was [a] really long wizz – like when you’ve had a lot of beer.
1997–2001		Online Sl. Dict. 🌐 whiz [...] n 1. urine. (‘He got whiz all over himself.’).
1999		N. Cohn Yes We have No 224: They’d walk into the khazi to take a whiz.
2003		N. Green Angel of Montague Street (2004) 186: Don’t touch your thing unless you hafta take a whiz.
2013		T. Robinson Hard Bounce [ebook] ‘I gotta take a whiz and you got his head in the urinal’.

In phrases

take the wizz (v.) [var. on take the piss (out of) under piss, the phr.]

to tease.

2000

Indep. Rev. 26 May 4: Here everyone just takes the wizz out of me for not doing a proper job.