I've got an idea on how to make a simple one out of brass;
Make a simple jig to hold the tubing, then drill straight through (rather than just one hole on the face.) Rotate 90 degrees and slit it with a jigsaw, then solder a strip of brass down the middle. Fill one end with solder on only one half of the tube, then the other side, fill the other half with solder. Slip into your PVC and one end is exhaust, the other intake.
Thoughts?