the overflow pipe
 

I know the overflow pipe in your 9 plant garden can go anywhere on the system. My question to you is how do connect the other end of the overflow pipe to the reservoir if your system isn't sitting on top of the reservoir? My guess is a hose of some kind?

Yes you can use flexible hose or add PVC fittings and pipe to run it anywhere you like. Sometimes I even put the tanks outside of the grow room and run the overflow and pump hose to the garden.