Apparatuses are provided to facilitate sensing fluid within a fluid system, such as a coolant-based cooling apparatus for removing heat generated by one or more electronic components. The apparatus includes a plug configured to couple to a wall of the fluid system at an opening in the wall and to form a fluid-tight seal about the opening. The plug includes a fluid a fluid-sensor-receiving space configured to receive a fluid sensor, and when the plug is coupled to the wall at the opening, to position the fluid sensor at the opening in a manner to facilitate sensing of fluid within the system. The fluid sensor is removable from the plug without requiring uncoupling of the plug from the wall. In one implementation, the fluid sensor is a proximity sensor, and the plug is fabricated of a non-conductive material, and the wall a conductive material.