Mandrel testing also known as deflection testing is used to determine that the ovality of flexible sewer pipe meets design specification. This testing is critical to the long-term performance of PVC sewer lines being installed today.

The next inspection is with a mandrel. A mandrel is a device that is pulled through the conduit that is used to verify that there is an adequate clearance through the conduit.

Light-weight aluminum deflection are used and utilize a nine-fin configuration, allowing for the passage of sewage when testing live sewers. Rings are used to verify that each deflection gauge is within tolerance.