The plumbing follows the design illustrated in the Woodcraft article ''Adding A Pre-Separator To Your Dust Collection System'' derived from the book Controlling Dust In The Workshop. The exception is that I used 4 inch PVC pipe. The center pipe extends 10 inches.
The upper pipe joints are cemented with Harvey's MP-6 PVC cement. Although not illustrated in this photograph, sheet metal screws are used secure the lower joints, and three single-hole right angle brackets were used to anchor the Elbow; to prevent it form rotating.