Eugene,
Once again, I have been a great fan of this tank for some time. I hope this isn't too wordy or out of line.
In designing and testing my herbie overflow, I keep coming back to three key factors. These are seals, head height and aesthetics. The first is obvious - your tank will drain to the lowest exit point, if your overflow box isn't sealed, the entire thing is all but useless. Full length weirs have the disadvantage of having either seals that are longer than they need to be or wasted/hard to reach space at the bottom half. The obvious counter argument is that they make for a cleaner, less distracted look.
I drafted several "full length" weirs and overflow boxes but eventually decided on a smaller one for a couple reasons - its cheap/easy to make and install, reusable as its not sealed to the tank itself, less acrylic I will have to scrape coralline algae off of in the long run and finally, smallest visual foot print in the tank.
Included is a picture of my prototype which is about 2x3x5 1/4" and houses two 3/4" bulkheads - its been tested at ~300gph silently (though it will handle much more, expect more rise in the tank water level to create enough pressure to flush the siphon) and I even have an egg crate insert that I use to hold pre-filters made out of old filter socks - though they gunk up faster, there is much less surface area for bacteria/phosphates to accumulate than a filter sock and they effectively keep junk/snails/dead animals from clogging the impossible-to-see pipes.
http://i21.photobucket.com/albums/b269/misterchezpt/SSC_1783.jpg
hope Ive been helpful!
-Peter
