Green’s Dictionary of Slang

urination.

2001		OnLine Dict. of Playground Sl. 🌐 wiss, wizz, whizz, wass n. urinate, to have a piss. As in ‘I’m going for a wazz (etc)’ – I’m off for a piss, or ‘we were having a wazz.’.
2002		(con. 1983) D. Peace Nineteen Eighty-three 276: I went over Ditch to have a waz and that’s when I saw her.
2006		D. Mitchell Black Swan Green 322: Just off to the wood for a waz.
2017		Times Times2 6 Jan. 🌐 Festivals [...] don’t seem the obvious place to take out a special Rita Ora-branded cup, squat down and have a wazz.