If the level in the tank drops below the location of the pin hole then the siphon will stop, but there will still be water in the tube that goes over the side of the tank. So either I am completely out of my mind with this
or the siphon should restart when the tank refills.
The problem is: when the pump /power is off the water level will decrease. As that occurs air will begin being sucked into the system via the pin hole. If there is enough air in the main overflow (where it actually goes over the tank rim) when the siphon is broken--then the siphon will actually be broken--completely, and it will not restart. The water in the main overflow portion must be maintained during a power outage--or the siphon will not restart. Hope this makes sense.....
I use the pin hole for the inflow/pump return line. It works great. I have a check valve also, but with the pin hole--the check valve really isn't necessary. The pin hole is at the water line (full) so when the pump turns off--the siphon is immediately broken. The water in the line drains back to the sump and that's it for that line. Prevents siphoning the tank into the sump via the drain line at power off.
The DIY PVC Overflow works very well as it is designed. There is a "skimmer" version, but that starts adding more "pretzel" inside the tank. One simple modification that I made was adding a cap and air line:
Pix are clickable:
This makes the system quiet.
You can DIY an overflow/skimmer box system like they sell and it can be done cheaply out of plastic containers and pvc. I did it a couple of yrs or so ago. But you wind up with more stuff in the tank, its gaudy and there really isn't much point. The overflow above works well. Only complaint would be slow flow--but for me its fine. I guessimate that the 1" pvc overflow that I use moves ~100gph. Maybe a bit more. But its on a 40g tank (2.5x/hr) and the tank is directly filtered with an xP3. So, its really not an issue for me.
I started out with the drilled hole concept for the strainers. Depending upon all the variables--they may clog or partially clog over time. I went to one of these for the overflow strainer (only because I had one from another project laying around), but if you have a miter/chop saw--they can be made very easily with pvc.