Words for rain: Raining cats and dogs. Two rather more colourful expressions which I quite like are 'it's raining stair-rods' and 'it's raining pitch-forks'. It is difficult to see where the business part of a pitch-fork comes into play, unless it describes the angle at which heavy driving rain bounces back from a hard surface.
I think I have heard almost every bodily function involving a fluid used to describe rain, such as pissing, spitting, crying, etc. Similar to the nasty weather being given human characteristics that was discussed a while ago on the show (caller from San Diego who was a fisherman).