Bart,  I assume you are trying to build an 'Epiphany Pipe' from John
Kleinbauer's design.  I myself experimented with the pipe as designed
without great success (which was probably due more to my lack of proper
tools at the time than anything) and finally tried combining the fipple
plug with a more traditional pipe mouth.

Rather than drilling into the PVC at right angles, I cut a slot across
it and slowly shaved away the plastic above at a fairly low angle,
10 degrees or so, resulting in something not unlike a traditional pipe
mouth.  This, of course, meant the lip of the pipe was both curved
upward and bowed out with the shape of the PVC.  Surprisingly, with
careful adjustment of the fipple and fine-tuning the mouth
height/shape, the pipe spoke easily, and with quite a bit of volume.

I might also mention that due to the un-adjustable diameter of the pipe
(un-scalable), it is fairly easy to make a pipe too long out of narrow
PVC so that it won't speak as well.  I tried to keep my first pipes
short, under 8 inches or so when working with 1/2-inch pipe.

In my experience, pipes can be tricky to work with, but I gained a lot
of practical knowledge on pipe building and voicing while experimenting
with this design.  Good luck!

Ben Willis