A conduit proving mandrel is a tool used to verify the roundness and shape of a conduit, typically after it has been filled with a material such as soil. The mandrel is inserted into the conduit by blowing air or pulling it through with a fiber rod and attached draw rope. The mandrel is then pulled back through the conduit to inspect for any crushing or deformities. To ensure it can be easily retrieved, a secondary draw line is attached to the other end of the conduit. Conduit proving mandrels come in various sizes for different conduits.