[neatoman]

Well for what it's worth, most sewers in real life aren't much like what is depicted in fiction. Generally speaking, the tunnels mainly just exist for the purpose maintenance work, the actual sewage is typically contained within pipes. It's more like a basement than an underground river. There are exceptions to this, the London sewers are so old the sewage is transported by brick tunnels rather than pipes, but I'm not sure New York is one of these exceptions.