Rebreather left in cave as part of ongoing project. Oxygauge removed but blanking plug forgotten - so hole in one counterlung. Rebreather hung from wall approx 10 feet above level of sump pool covered over to prevent spray dripping in. Next visit. Signs of previous high water but rebreather apparently undisturbed. Kit reassembled and breathing checks undertaken without problem - but - breathing drill carried out pre-dive while sitting upright. As the diver assumed the prone position in the sump pool still carrying out the breathing drill he heard a gurgle immediately before receiving a mouthful of highly caustic sump water. It appears that the loop had partially flooded through the P Port in the counterlung with the scrubber and its water trap working so efficently that there was no sign when the diver was upright ie with the scrubber at the lowest point of the unit. Only with the water trap at the same level as the counterlung did the flooding become apparent. Previously there was no gurgling or sense of water in the system as the kit was handled and teh bretahing gas was not unusually flavoured.
Never leave a hole in the loop even if you think that the kit is out of harms way! Always carry out final breathing checks in the position that you will assume while diving. A caustic cocktail is one of those experiences from the past like ricketts and National Socialism that you really don want to revisit. Vomiting alkaline fluid through a throat constricted to half its normal size is no fun. Underwater rather than standing in the sump pool it would probably be an unpleasant way to die.