Rhyming slang for piddle. The act of taking a piss.
"Now you're trying to run my life again ain't you Del? Well,
if I let you get away with it this time I won't be able to go for a Nelson Riddle without you giving me a blueprint." (Rodney in "Only Fools And Horses" in Series 2, Episode 1: "The Long Legs of the Law")