: We just installed a new toilet and after flushing the toilet all the water in the bowls goes down the drain several seconds after it finishes flushing, leaving a very small amount in the opening only. Can anyone please tell me why this is happening?This is called self siphonage. As the water leaves your toilet it creates a partial vacuum behind it dragging the water from the bowl as it goes. Usually the toilet bowl outlet is smaller than the pipe it is connected to, this allows air to move along above the flowing water. Check that the pipe (drain) size is correct.(110mm). Check that the horizontal run is not too long. If there are vent pipes fitted check they are not blocked. If it is a single stack (one vertical main pipe) check that the vent potion is not blocked (birds nest are common).good luck…..john
