Similar design is working down at my LFS (which are also DIY jobs).
I've actually changed the design from the photo becuase there wasn't enough pressure for the syphon to work if the outlet came from the top of the unit (which is what most people do), due to the height of the tank compared to the size of the unit (100mm diameter about 500mm high).
I reduced the number of coils, and switched the inlet to the top and the oulet to the bottom. The unit is filled with bioballs and has to be pretty air tight because it's under pressure. It seems to syphon fine, but after a few weeks still no love... I may have to switch back to the original design if nothing changes.[/img]
