When I was a teen in the 70s the loo was usually referred to a the 'bog' also the guys would say that they were going to 'take a leak' or a 'slash' or 'splash their boots'. After a hard night on the beer they would often use the term for vomit as a 'technicoloured yawn'.

Being female I would refer to using the loo as 'spending a penny' which was refering to the days when you had to use a penny in the slot to access outside public conveniences, it has always stuck for some reason.