You set out to achieve an atmosphere with this piece and you certainly achieved that!
This would be a great intro or menu screen kind of soundtrack. Excellent work on getting each sound to play its role in this. It makes me think of literally being down in a sewer because of the sounds you use. Looking around each corner expecting to see something you probably don't want to. A dead goldfish, half eaten carcass, or maybe even the things that live in the sewers.
Great work! 5/5!
-DareDevil424