Well, there's not much to it - it's just 1/2 inch pvc pipe, 3 L's, 2 T's and a bottle. In this example the bottle was just a quart, but for a larger tank, I use a liter. I cut a hole in the side and top of bottle and superglue mesh fabric onto the side of it. Then superglued the bottle onto the pvc pipe.
Next, set it in the tank and get it to 'balance'. I use a wire and 2 magnets. Then, place an airline hose down the first tube. Push it all the way down and then pull it back about 1/4". Start the airpump and a suction will be created. Place a small light on the outside of the tank and at the bottom of the first tube where the airline tube is. Then, turn all other lights out. The larvae will be attracted to the light and then will be sucked up in the tube and stored in the bottle.