So here you can see where I drilled the hole, I only took a picture before I drilled the air input hole but you get the idea.
In this picture, the hole would be in between the lip on the inside of the bushing and to the right of the right-most glue ring.
Here you can see how I filed off the pipe stop so the pipe can extend in the horn body, like when you make a piston valve. Right behind the lip is where the air hole is.
