...but the tanks themselves were difficult to climb up to and very difficult to close. The lids were heavy. Getting purchase on them one floating in water inside the tank would have been very difficult.
So, which is it, closed or open? There are gaps in the story, but they appear to be gaps in the retelling, not necessarily in the investigation itself.The official story has the hatch open when the maintenance man found the body. The cover was apparently not hinged, and was sitting on the top of the tank, off to the side.