This is what I made a long time ago. It worked ok, and pulled a lot of stuff out of the water, I've been using a refugium for a long time, so I do not use it anymore.
It was basically a counter current protein skimmer, the water would come thru the opening where the arrow is, and come out on the other 'side' because the opening was higher than the top of the reaction chamber.
The line with the air stone is conected to an external air pump, and the water is pumped from the main tank.
Hope this helps.