If you have access to a laser cutter, I think you should probably just go to your nearest LFS, and threaten to vaporize whoever is working there unless they give you one for free.
But if that doesn't work, its not all that complex.
basically in a sump, you have a wet/dry chamber, which means water trickles over the media instead of covering it completely.
I made this extremely detailed rendering of a wet/dry sump for maximised learning efficiency.
water comes in on the left, through the orange pipe (which is usually pvc) The first chamber fill up, and water flows over the top edge into the next one. The green lines is a drip plate, which is basically a sheet of plastic that has lots of little holes. Water spreads over this and drains down through the biomedia (usually bioballs) which is the yellow. The orange dotted line is basically like the green one, but with more holes, so water can drain out the bottom of the biochamber. The water level in this part of the sump is near the bottom of the chamber of bioballs. The pink thing is the pump, which pumps water back into the tank.
The blue bit is the water, BTW. And this is a side view.
I seriously spent like 9 minutes on that drawing (which is copyrighted by FSM inc.)
I deserve a prize.
