I used a low flow toilet in an apartment that had been vacant for some time, and a toilet that had not seen much use. The bath in this area was never used. My recollection was that I flushed the toilet, and stayed around the unit for another 30 mins. without hearing or noticing an overflow. After leaving to the gym for 2 hours, I came back to find the apartment totally flooded to the extent that it flooded( or seeped to 2 I had heard gurgling in the past upon flushing. units below me). Only yesterday in my lease did I see mention that low flow toilets can overflow. Please provide me an explanation for this, and causes. Thank you.