It's interesting how the english version only notes the official report, and puts the alternative story in a single sentence. The german versions also reads (before citing the official report):

"When the Commander, Lieutenant Captain Schlitt, operated the flushing of the toilet on April 14th, he ignored an order according to which the flushing was to be triggered exclusively by the specialist on board.

Sea water, mixed with Schlitt's excrement and urine, poured into the submarine at high pressure through the open valves.

The toilet specialist was no longer able to close the toilet closures. According to reports of a survivor, the boat sank 'like a stone' into the depths."

To the incident itself: Shit happens. (scnr)