I installed new toilet system and while I was away for the day that overflowed and flooded the basement. The engineers report says that "the toilet was blocked and the internal overflow flooded the basement. I had to restart the failed unit overflow". Apparently the soil pipe outside bathroom was blocked and this caused the toilet to overflow onto the pan. I'm trying to get the plumbing contractor to accept responsibility, but he is saying that I must return to my own. He is saying that the drain was blocked (not put back in) and it overflowed back into the toilet. What do you think. I was happy to learn … I recently had a new toilet installed. The manufacturer had two sets of mounting hardware at the base, but our installer just searched and pulled out a set. Consequently, the toilet was constantly locked until you call the plumber and had reinstalled. So even with the lock never overflowed. That's the part that makes no sense in the story. No matter if the toilet is blocked if the water is not running. It sounds to me like the "defective overflow", which was installed by the plumber was the cause of this problem, there is a blockage in the pipe. I think the plumber's insurance should pay. The plumber would be on the hook for water if the toilet had kept running and drainage only.