So apparently that piss smell wasn't actually from the open sewage.

It was because before cars took over horses were the primary mode of transport for people who could afford it, and horse piss is absolutely rancid smelling if it lands on something that doesn't just absorb it like dirt or soil.

Local oyster place chunked the shells outside, covered the parking lot in fact. Attracted quite a feral cat population, but it didn't stink.

Also, I think you're confusing modern "stink" vs. 1800s NYC "stink".