Maybe this will help
Left to right:
Main and emergency drains with a tap for a filter sock
Skimmer and pump, which drain to the middle refugium area.
Final chamber holds the return pump.
The GFO/Carbon reactors over the refugium are powered by a manifold taken off the return line.
The 3 pieces of tape mark the low level water line, high level water line and the max water that drains when the pumps are turned off.