They are very common and found scattered across the wasteland, normally found in toilet stools and toolboxes.
Inside the DC ruins hides an unusual room. This room is located inside the shelter and holds multiple plungers, a single feral ghoul, and bloody hand prints decorating the walls and ceiling. Curiously, these handprints seem to have six fingers instead of five. One can also strangely be found inside a safe at Smith Casey's Garage.