John - I was part-joking about the East Canal solution, and I certainly hadn't thought about the pressure issues involved, so thanks for pointing that out. But I guess if it had been full it would be possible, theoretically at least. I've never seen the downstream end of Treasury, owing to the levels being a bit fierce last time I was down there, and we bailed just beyond Window Inlet, so I've no idea what the passage profile or inclination of the sump connection is, or whether a buoyant object could 'bump' its way along the roof and into Peak. It sounds as though it's a possibility though from your description. Do you have any photos of the downstream end passage, out of interest?