240dl
Unfortunately I don't remember the tour specifics well enough to confirm the exact use case of the system.
You might also enjoy some of my other drain exploration shots from stateside:
The guide himself was free, a nice older gentleman who used to be some sort of government liason. He insisted on taking a taxi for the 2 miles from the train station to the tour though, which was pricey. But I didn't have much of a choice (despite a whole face-saving false choice he offered of walking vs taxi that was deeply emblematic of a certain strain of Japanese cultural weirdness).
http://www.lucashayas.com/journal/2018/11/18/maoudc
It cost about 80 bucks all told and was a bit of an ordeal to organize (you need a fluent Japanese speaker), but was definitely an experience. It was a little disappointing in how limited our tour was. I get the sense that they've narrowed down the area you can wander since opening. Still, I've explored storm drains in the US quite a bit and this was a whole different level.