Cut an empty paper towel roll in half, down its length. This will form the main body of the parabolic collector.
Fasten the two halves of the paper towel roll together with brass brads. Position the two halves of the roll back to back, so the concave faces are facing out. Push the brads up through the two halves from the bottom of the structure created, so the prongs are on top.
Coat the top half of the apparatus with rubber cement adhesive. The adhesive should dry to the point that it is sticky, no longer wet, before going on.
Cover the top half of the apparatus with aluminum foil, with the shiny side of the foil facing out. The adhesive will join the two surfaces. Get the surface of the foil as smooth as possible to increase the efficiency of the final solar collector. You may need to cut small slits in the foil to slide over the brad prongs.
Bend the prong ends of the brad around a pencil. The prongs must form complete loops. The aquarium tubing will run through the loops created to hold it in place at the center of the parabola.
Run aquarium tubing through the two rings created by the brads. There should be an equal amount of tubing hanging off of each end of the paper towel roll, with the middle section affixed to the roll by the brads.
Use the sharpened end of the pencil to poke a hole through the side of the polystyrene foam cup about a half inch up from the cup's base.
Slide one end of the aquarium tubing up into the polystyrene foam cup. The tubing should fit snugly in the tube. The solar collector will not work correctly if the opening is too wide.
Press plumbers putty into the area around the aquarium tubing on the face of the cup. The plumbers putty will seal the union and prevent leakage.
Set the2 by 4 and the 1 by 4 boards on a raised surface like a table top. The blocks should be set against one another to create a stair-like surface.
Set the parabolic collector on the center of the 1 by 2 block.
Set the polystyrene foam cup in the center of the two-by-two block.
Place a short jelly jar or other small dish on the table surface directly below the end of the aquarium tubing. This dish will be the collection point for water running through the system.