In this paper, we analyze the behavior of Storm Drain Pipes (SDPs) as multi- mode leaky waveguides for radio wave transmissions between 2.4{2.5GHz within the Industrial, Scientiflc and Medical (ISM) band. The previous research on analyzing RF propagation inside underground structures focused on auto, railroad, subway, mine and sewer tunnels of diameters greater than 1.05m. Our research provides a novel contribution by characterizing RF propaga- tion inside narrow SDPs of diameter as low as 0.30m. Understanding the behavior of SDPs as communication channels is not only important for designing portable military communication equipment, but also for other civil applications. We study the modal content of propagating waves and derive a mode based model (MBM) for predicting the received power. Empirical data gathered at selected sites in Charlotte, North Carolina is used to validate the MBM. Based on analysis of nonlinear curve fltting through the measured data, close agreement is found between the predicted and measured power. We also highlight the requirement of further work to improve the fltting of measured data with the predicted results.