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A likely cause is that the building is located near a junction of sewer mains which, once blocked by the ice, forced the hail through the routes of least resistance: the indoor plumbing.
Silvia Streit, a resident, displayed a great sense of stoic resistance. "I grabbed a board and put it over the toilet, but the pressure was so great I ended up sitting on the board as the hail flowed through the flat and down the stairs."
Compare this reaction to that of Martin Bierbauer, another resident, who was on his pan at the time. "Suddenly hailstones the size of golf balls started exploding out of the toilet like a popcorn machine. There was an avalanche of ice that filled the toilet, then the entire flat. I ran downstairs with the hailstones following me, and other residents did the same."
This was definitely an unpleasant event: having fecally-covered icy grapeshot shooting out of your toilet is scary. But this is also an interesting reflection of modern society these days. Look at the reactions: Silvia metaphorically hoisted up her undies and took personal responsibility to limit damages with her sturdy wooden plank. Martin, however, just stood there, trousers around his ankles, watching as the festering, frozen mess consumed his bathroom. Then, as he admitted, he ran away.
Martin is now demanding substantial damages; yet he was unwilling to do anything to help while the event took place. I know which of these two I'd want on my side if this sort of toilet terror happened to me.
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