The Cord Seal Fitting is a nifty gadget that addresses that particular need, to pass a cord through the wall of a reservoir inside the fitting or pipe that is the reservoirs only perforation. It works much like a plumbing pressure test plug. A rubber gasket squeezed between two plates expands outwards and seals off a 1-1/2" female socket. But, unlike a test plug, the rubber doughnut is slit to its center to accept a standard light or pump cord. The plates on either side of the gasket are also split, to assemble around the cord and gasket like the cookies around the creme of an Oreo. When tightened, the rubber expands tightly around the cord and into the fitting, creating a waterproof seal.