This is a small reed instrument with a mighty deep voice for its size. It belongs to the Tootophone family, of which I am the father (see: https://www.instructables.com/id/pvc-TOOTOPHONE-a-musical-reed-instrument ). You might call this one Baby Bass.
The rubber reed is a new variation, one that gives it the deep voice. It is not as springy as stiffer plastic reeds, and is probably a little heavier. That makes it vibrate more slowly and create lower pitches. The reed is made with a new clay-like rubbery product called Sugru.
The silicone rubber cartridge body adds resonance and volume.
It is intuitively easy to play, with no fingering. Be sure to click on the .mp3 file in the last step to hear how it sounds.
Step 1: Forming the Mouthpiece
The mouthpiece is made from the plastic tubing of a discarded ballpoint pen. The original angle cut can be made with a saw, or just sanded down with heavy sandpaper.
The most important part of the shaping is the curve in step 2 of the diagram. By having a continual curve, instead of a straight cut, the reed will always form a tangent line when the player's lip presses it to the body of the mouthpiece. The reed must have room to vibrate in order to make sound. Shorter vibrating sections will vibrate more rapidly and make higher pitches.
Shape the curve by pressing the tubing down on sandpaper, pushing it forward and back in a rocking motion.