Oh Jesus, I remember diving Crescent. Probably the most idiotic project I ever managed to persuade some people to carry for. If I remember right, Adam Cooper, Jon Watt and Phil Howson made up the team of heroes.
But...the line in there is not mine. I was also surprised to encounter that line (which I believe was laid by Phil Papard in what must have been high water) and got some distance beyond before diving gear was strictly necessary for the water conditions on the day concerned, which from Tony's description I would guess were perhaps "medium". I was doing this dive on a base fed line which ran out after 25m. It would have been theoretically possibe to get further if one of the sherpas would have been willing to come nose up along the bedding and then hold the line. Not surprisingly there were no takers for this task!
Obviously because the bedding is so horizontal, a small change in water level means that the water moves forward and back a long way, making it hard to reach any kind of agreement on where the sump actually starts. Unfortunately a horizontal bedding such as this tends to contain gravel and mud banks, making the whole exercise pretty unpleasant.
It is an excellent trip, but choose a day with good weather. What was very noticable after the trip was that my wetsuit was absolutely shredded on the shoulders and hips. The most tiring aspect of the cave in my view is the amount of crawling in low letter-box shaped passages. Not really tight, but sustained and extremely arduous.
Unless Tony has any information to the contrary I believe that the sump is still open at the end. So if someone is looking for a project....
Mark