Aqua Clear Aquatics Pro 75 Wet/Dry filter w/ skimmer

[Ampalmer]

Hi- I am trying to put together a tank for my sons science classroom, I have a Aqua Clear Aquatics Pro 75 Wet/Dry filter w/ skimmer in pieces, but I think I’m missing a few. I can’t find good instructions anywhere. I am missing a pump for the skimmer, and I can’t figure out for the life of me how the water gets from the skimmer section to the trickle down filter section. Does anyone have this set up who would be willing to give me a little advice?

[Ampalmer]

More pictures

[Fresh2o]

I Googled this filter but could not find any with the same design.
Regarding the skimmer, I’d imagine the pump that feeds it sits in the first chamber (on the left) and is connected to some tubing (not pictured) that fits into the hole halfway up the skimmer body. The discharge is at the bottom where the black barbed fitting is. Why tubing is connected to it I’m not sure. Anyhow, the skimmer discharge mixes with the incoming water from the tank which leads to a foam prefilter sitting in the tray above the bioballs.
The return pump looks like a submersible Danner Pondmaster Mag X pump. I would swap out the brass fitting with an appropriately sized plastic adapter.

[Fresh2o]

Please excuse the Madden style telostrater arrows