A drain disinfecting device for disinfecting the internal surface of a drain pipe wall that is provided with a hole or aperture includes a UV LED module provided with a transparent lens through which UV-C light can be transmitted. The module is attached to the drain pipe to register the transparent lens with the hole in the drain pipe to transmit UV light through the transparent lens into the interior of the drain pipe to irradiate the drain pipe inner surface with UV light. A watertight seal is provided between the drain pipe and the module. A controller is provided for selectively energizing the module. A method of converting an existing drain pipe to disinfect the interior surface includes forming a hole or aperture in the wall of the drain pipe and registering the drain disinfecting device with the hole or aperture in the drain pipe.
