The adj filthy has 3 senses (first 1 from tagged texts)
1. (2) filthy, foul, nasty -- (disgustingly dirty; filled or smeared with offensive matter; "as filthy as a pigsty"; "a foul pond"; "a nasty pigsty of a room")
2. dirty, filthy, lousy -- (vile; despicable; "a dirty (or lousy) trick"; "a filthy traitor")
3. filthy, foul, nasty, smutty -- (characterized by obscenity; "had a filthy mouth"; "foul language"; "smutty jokes")