It is a very nice map. I am a big fan of sewer systems. I assume this map is intentionally designed in a labyrinthine manner for plot purposes.

Just as an aside, more realistic sewer systems are generally (there are always exceptions) built very similar to how rivers work. They have a tree-like structure and the size of the pipes is bigger depending on the volume of fluid they carry because, like rivers, they are gravity driven. And they usually empty out into a swamp, river or the coast.