Here is a great link for Hang on the Back Overflow boxes. I used this when I built the one I had on my smaller tank. It worked great but there are dangers involved in this type of overflow.
http://www.melevsreef.com/acrylics/overflow.html">http://www.melevsreef.com/acrylics/overflow.html</a>
Anything you find on [IMG]http://www.melevsreef.com/">http://www.melevsreef.com/</a> is worth it's weight in gold.
Here is a link on several types [IMG]http://www.google.com/search?q=durso+overflow&hl=en&rlz=1R2ADRA_enUS463&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=P2AhUOvLGYPA8ASG04DIBA&ved=0CFsQsAQ&biw=1024&bih=658">http://www.google.com/search?q=durso+overflow&hl=en&rlz=1R2ADRA_enUS463&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=P2AhUOvLGYPA8ASG04DIBA&ved=0CFsQsAQ&biw=1024&bih=658</a>
Durso is the most common type. In my earlier post I gave you a link to the Bean Animal style. Given a choice, I would never go with anything other than the Bean Animal myself.