Green’s Dictionary of Slang

to urinate; also as n.

1890–1904		Farmer & Henley Sl. and Its Analogues.
1980		Barltrop & Wolveridge Muvver Tongue 42: The other function is a ‘Jimmy Riddle’, a ‘leak’, a ‘you and me’, (rhyming for ‘pee’); or ‘sip’, noun or verb, which is ‘piss ’backwards.
1992		R.G. Barrett Davo’s Little Something 13: ‘Luff of sipp’ [meant] full of piss.
2001		J. Burkardt ‘Back Sl.’ Wordplay 🌐 sip: piss.