On April 14, 1945, the German submarine U-1206 found this out the hard way.
Who Fucked Up?
That model of boat had a new, fancy toilet-flushing system that used a complex system of high-pressure valves to allow them to flush the toilets even when running deep under the sea. So complex, that you couldn't operate the system without supervision.
But the captain of the submarine, Karl-Adolph Schlitt, figured he would chance it. After all, it's a damned toilet! How complicated can it be?
One splashing, cursing, Charlie Chaplin-esque slapstick sequence later, and Schlitt found himself wading through the Atlantic seawater that was quickly rushing into the submarine. Unable to pump the water out, Schlitt had no choice but to surface the sub.
Of course, this was in the middle of a war. Oh, and the German submarine just happened to be on a spy mission just 10-miles away from the British coast. It was almost immediately spotted by an English plane, which proceeded to bomb the shit out of the sub. Schlitt found himself unable to escape and gave the order to abandon ship, where every surviving member of the crew was captured.