Thanks to an information trade with a member on here, I was able to locate said drain! I was able to find a relatively non suss place to park, since it was pretty early into the night and made my way to the entrance. Walking along the RCP, I thought I must have taken a wrong turn since only junction rooms and a car door were present to break up the piping. Eventually I came to the expansive tunnel I was expecting.
That was after finding a massive snake :shock: It was dead but still gave me quite a fright..
Walking onward, I found the feeder pipes. I could hear a gathering going on at one of the adjacent houses so couldn't get a decent photo without being too obvious with my light. Probably overly precautious, but meh..
I walked further along and found a random boarded up side pipe..
Even further along I found a waterslide! Needless to say, it was interesting climbing up it..
Further on the tunnel became almost crawling height so I decided to walk back. I Made it out without a commotion, but it sounded like the 'gathering' had moved out into the park above the grate..