the pipe does NOT come up at one end of the raceway and empty at the other. When I was trying to put this all together I figured I'd need to have the raceway take care of the skimmer(s) as well, so 80% of the north leg of the raceway was going to be for the skimmers and they were going to go back to the lake through a couple of four inch lines that are at the east end of the north leg of the raceway...
in this pic I inside the raceway at the west end of the north leg. the pipe right up close is the 6 inch feed from the vortex...you can sorta see the two four inch pipes at the other (east) end. They have four inch ball valves on them..and are never used. well let me say the 4 inch ball valves are used all the time...to keep water from going out the pipes.
also if you look on the right wall you can see blocks stuffed in the two "skimmer" holes about 15 ft apart.