Take your 1/2" pipe. Take your hacksaw. Cut about 5" off one end of the 1/2" pipe. The trick ts to cut the pipe at an angle of about 20 to 30 degrees. The exact angle isn't important. I cut mouthpieces freehand myself. And I can only approximate an angle of 20 to 30 degrees since I haven't owned a protractor since I was in 10th grade.

What you'll end up with is a pointy, short piece of pipe that resembles the tip of a giant hypodermic needle. If necessary, trim the mouthpiece length down to size so that it measures 3 1/2" to 4" from tip to base.

Now you want to smooth out the surface that you just cut so that the rough saw marks are no longer visible. Use 120 grit drywall & plaster sanding screen -OR- 120 grit wet/dry sandpaper on a flat surface(like an old glass tabletop) to do this. Wet the abrasive with water. This helps keep the plastic from melting and clogging the sandpaper. It also keeps the fine PVC dust from ending up all over your clothes, floor and in your lungs.

Sand in an up and down, side to side or circular fashion. It doesn't matter. It may take a bit if elbow grease to completely sand down all the rough grooves left by the saw blades. When it is completely free of saw marks, set it aside and move to the next step--->