Green’s Dictionary of Slang

whiz v.²

to urinate.

1929		D.H. Lawrence Pansies 17: I wish I was a gentleman As full of wet as a watering-can To whizz in the eye of a police-man .
1968		Frank Zappa ‘Let’s Make The Water Turn Black’ 🎵 Whizzing and pasting and pooting through the day.
1973		S. Ace Stand On It (1979) 221: Lissen: I really got to pee [...] You gotta stop and lemme whiz, you guys.
1987		(con. 1968) Bunch & Cole Reckoning for Kings (1989) 217: A woman’s gotta whiz when a woman’s gotta whiz.
1997–2001		Online Sl. Dict. 🌐 whiz v 1. to urinate. (‘I’ve got to go whiz.’).
2003		T. Dorsey Stingray Shuffle 283: He [...] produced his penis from the layers of plastic and whizzed on the canvas.
2007		Skins ser.1 ep.2 [TV script] Christ, I wanna wizz.

In phrases

whiz jism (v.) [jism n. (2)]

to masturbate.

2003

Number One Adult Sexual Health Terms Advisor 🌐 Masturbation Slang Male Terms: [...] whizzin’ jism.