Rainy "season" in SF? That's January, and the past few years even January had been pretty dry.
That is in fact why I think SF has a bad rap for being dirty: it doesn't rain very much. I've lived in SF since 2007, before that I'm Chicago for 14 years. I was recently back in Chicago for a few weeks. It gets just as dirty as SF or any other city, but it rained three times in a single week in Chicago (two with tornado warnings), which does wonders for washing away just about everything, including all kinds of smells, detritus and (human or otherwise) excrement.
