Step 1: Stuff I Used...
One air horn. One air wand. A coupling and a 2 inch long piece of threaded pipe.
From there just a couple wrenches and Teflon tape to seal the connections.
No actual sizes are given because there are so many possibilities. I think my parts were just 1/4 inch course thread....
Step 2: 10 Minutes Til Fun
Step 3: No Pic Necessary
These air horns are also pretty loud! They were designed for trains, large vehicles, or even as alarms. They have a decibel rating at 120 and higher. This can cause temporary or permanent auditory failure (makes some one go deaf).
When/if you use this never direct the bell (open end) towards a person and make sure they are healthy enough to take a scare (funerals are expensive at the very least).
I built this and showed its functions as proof to my coworker that he wasn't going to like the way I was going to save his job (sleeping gets you walked out).
I think this Halloween I will use it to scare some people as well.
I think this took me about 10 minutes to throw together from stuff I got at the swap meet (maybe 15 bucks..?) but I'm sure it'll be worth much more in laughs alone!
Enjoy and be safe!