A double wall pipeline is provided for a pumping system for fluid products, such as gasoline, diesel fuel and chemicals, and including a pump for pumping such products from a storage tank through the pipeline to a product dispenser. The double wall pipeline comprises a double wall, an inner primary pipe, an outer secondary pipe spaced from and surrounding the primary pipe, and integral spokes or spacers for supporting the secondary pipe in spaced relation to the primary pipe so as to create an annular space therebetween. The ends of some of the secondary pipe sections are stripped or cut back so as to terminate short of the corresponding end of the primary pipe and thereby permit testing and inspection of the primary pipe prior to completion of a secondary piping system in which the secondary pipe is incorporated. Unique primary and secondary fittings are provided as well as an air test clamp assembly for testing the integrity of the primary pipe and a collection sump fitting incorprated in the pipeline to permit the location of a leak to be visually determined.