My instrument is the Trombophone. It is made of rubber tubing, plastic tubing, a tin funnel, trombone mouthpiece, and electrical tape.
The rubber tubing was used for holding everything together as well as providing a soft and comfortable grip. The plastic tubing (on the inside) serves as a resonator. The tin funnel adds resonance and helps project the sound. The mouthpice is used to help your lips to vibrate. The electrical tape is mostly for decoration but does help to keep the mouthpiece attached.
My Dad and I started by purchasing a 6 foot rubber hose and the tin funnel. These two pieces alone did not make a very good sound. So we inserted a plastic tube to make the sound more vibrant. Then we added holes to tune the overtones.