any one know how this guy did this?
This looks a lot like the one we initially made for the nano a few years ago (love those acrylic hang on boxes). Basically he drilled one fo the large hang on boxes and put a bulkhead in the bottom. The part hanging over the tank is a J-tube that was long enough on the short end to sit below the bulk head opening (you can raise the water level by adding a pipe to the bulk head. Adding a U at the top
might eliminate the need for that rod - not likely to work for long - to keep the gurgling noise down). The long end of the J-tube must be long enough to never come out of the water.
This set up works as long as the fine tuning stays in place (ours would have to have attention several times a week). The biggest probem comes in the balancing act Robind mentioned with keeping water levels equal.
As shown, the water level in the overflow box, at its lowest, will be below the water level in the tank and high enough in the overflow box to maintain the siphon. If the water in the tank evaporates (we see 2 gallon a day evaporation with some of our tanks when we have to use cooling fans) or you do water changes that bring the water level in the tank below the water level in the
overflow box the water will reverse direction (siphons will always try to equalize the water levels), empty the overflow box and break the siphon. We experimented with different ways to avoid the problem but never succeeded in a trouble free set-up.
Our best effort was to take a large diameter PVC pipe the full height of the nano, cap the bottom and add a tee and hose barb and then another piece of pipe to the top and put the J-tube (J-tube and hose diameters must exceed the pump capacity). I don't have a picture of the set up but you can see from the photo (note the belt I sacraficed for this use) that we never really found a great way to attach it.
The nano was inactive for a couple of years and when we set it back up, we dispensed with the sump but it only houses a matis shrimp and some polyps now.