
Opening A 200-year-old Trapdoor Under Manchester's Rochdale Canal [video] - camtarn
https://www.youtube.com/watch?v=OZeXcH4hmtY
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camtarn
The small wooden trapdoor acts as a plughole for a short section of the canal,
allowing it to be drained into the culverted River Tib some 15-20 feet below
for maintenance.

The trapdoor itself can be seen at 15:00 in the video.

