Just a weird question that popped in my head, but since the only real space station in existence always keeps itself squeaky clean, I wonder how one that doesn't have cleanliness as high priority would look? In everyday life, the dirty and gritty look we are used to are influenced, if not created, by gravity. Obviously dusts fall down, but rusts and stains also forms on places that gathers water, which of course is influenced by gravity. In spacecrafts where there is no gravity to pull things, and no system to clean the air, where would the dirty stuff go?
Edit: to put in more context, I was thinking about near-future setting without sci-fi artificial gravity, where interplanetary space travel has become common and inevitably someone is going to have lower hygiene standards for their space travels (not necessarily not having air circulation system; some of the comments have pointed out that living in space basically impossible without it). And this question mentions space station, but I suppose spaceships can also be included.
So my question really is, if I want to a portray dirty, old, weathered, and badly maintained spacecraft without artificial gravity, how would I do that? Which places would get dirty, by what, and how? And how much can you get away with leaving things dirty until it starts to become serious health hazard?