Thanks for posting the video. Having studied it many times poor Mr Wright's actions still remain a mystery. He appears to be looking over a well constructed steel fence, having just arrived at that point and not, apparently, having previously dropped an item into the drainage hole. Then, for some reason,he goes to the end of the fenced off area, climbs, over the fence, and falls down the hole. Maybe he dropped an item into the hole earlier than indicated in the video and returned there some time later to retrieve it. A search of the contents of the drainage hole may help to explain what was in his mind at the time.