In his article in Pelobates 52 Steve Wray described some of the work that went into draining the sumps in Poll na g'Ceim. Since then sump 3 has been knocked out altogether and sump 4 temporarily drained so that all the necessary pipes could be moved into position. Because there is a small inlet between sumps 3 and 4 this refills but, with the aid of another dam, it has been possible to set up a siphon arrangement.
The arrangement of pipes that has been installed is shown in the diagram below.
Under normal to moderately high flow conditions the whole of the stream is carried in the larger, 4" pipe. The smaller 3/4" pipe is then primed by opening valve V at dam B. This allows the head of water from dam A to clear any air in the system. After a few minutes the valve is closed and water will then naturally be siphoned from pipe X through tee-piece Y an flow out at Z. The sump then takes a few hours to drain.