huladad, I was trying to build an overflow as well, after reading lots of threads and advice from the guys I now have a custom one built with the cpr design (no tube)
here are a couple of things you need to change
the part that goes into your aquarium (the prefilter box), you either need to have teeth cut into it so that it can get the top layer of water + it avoids fish n critters getting ito the box, OR you can just cover the top with gutter guard or such
other than that your prefilter box is fine.
the outter box (drain) is another story. The bottom part of this box NEEDS to be below the bottom of the prefilter box for the siphon to work correctly (don't ask me why, but its simply the laws of gravity). If you look at the FIrST pic that you posted, one box is lower than the other. you've got it done the opposite way, so if you can just switch the boxes ur fine.
The second is u need a baffle or a divider in the drain box. it works like this.
The divider will be half the height of the box. One half will be drilled with the hole for the bulkhead the other hald will be sealed.
The part that is sealed will recieve the water from the tube, when it reaches the height of the baffle, it will overflow into the other half (the one wiht the drain).
if for whatever reason the siphon stops, it will automatically restart (most of the time) because of this divider.
Other than that you are set.
oh yeah one last thing, it looks like your U tube is 1 inch, and your drain is 1 inch as well.
Drain should be bigger than U tube, to prevent overflowing due to blocked drain or such.
Hope that helped ya.
