The intake on the main pipe needs to be face down because this pipe acts like a siphon. The emergency pipe also works like a conventional overflow, and is there just in case the main pipe fails, either by getting air in it or by getting clogged up. This is done indirectly by controlling the volume of water going through the main pipe. It is set up so that only a trickle of water runs through it. The secondary pipe works like a conventional overflow.

The valve is used to control the volume of water through the main pipe. This is why you often see a valve used at the sump end. Under normal operation the main pipe runs like a siphon, in that there is no air inside it. The bean animal overflow is designed to be as silent as possible.