In order to certify that process and drain lines which had been used for transporting radioactive materials, and their surrounding environments, are now free of residual contamination, it is both desirable and cost effective to make in situ measurements during the decontamination and decommissioning process. A 4.83-cm diameter modular proble consisting of a liquid nitrogen reservoir, a preamplifier, and a high-resolution germanium gamma-ray spectrometer with flexible connections between the modules has been developed for the measurement of gamma rays in and around piping. The assembly is sufficiently flexible to navigate through a “3-inch diameter p-trap.” The probe design and specifications are discussed. Results from an application are presented.