Instructables user rog8811 set out to build a functional replica of an old-timey manual boating foghorn using hardware-store stuff. He shows you how to build the basic horn by cutting apart a PVC sink trap and hacking it onto an off-the-shelf air pump. Then he does something I’d like to see more of in my own and others’ project tutorials—he encourages you to make the project your own: “Go mad! Get as many plumbing parts as you can screw and glue together to make the sound path long and wider.” It sounds on both strokes of the pump handle cycle.