Sewer camera inspection in Centreville.

The median owner home in Centreville went up in 1990, and about seven in ten were built between 1980 and 1999. By then the line to the street was usually PVC with glued joints, which won’t rust through like cast iron or crack like clay. What it can do is sink. The trench was backfilled when the subdivision went in, and thirty years of settling can leave a low spot where water sits and paper catches.

The other half is trees. The ones planted along the courts and front walks when those subdivisions went in are full grown now, and Fairfax County’s wastewater office says roots work their way into open joints and cracks. A plastic joint that pulled apart as the trench settled is exactly that kind of opening, and once roots are in, the line slows a little more each year.

Only about one owner home in nine here predates 1980. In those few the pipe may be cast iron or clay, and on some built from the late 1940s to the early 1970s, Orangeburg: pressed tar paper that goes oval, then caves in. If nobody knows what’s under the yard, the camera goes in before any snake does.

Not every Centreville address drains to a county main. The county health department lists about 390 properties in 20120 and 20121 with an active septic record, many of them along Bull Run Post Office Road, Compton Road and Fairfax National Way. On one of those, the line from the house ends at a tank, and septic work is not something SwiftPro does.