An apparatus senses properties of a fluid. The apparatus has a pipe section, a valve, and an instrument. The pipe section has an envelope, through which a flow of the fluid is coupled between a tank of an electrical power device and a cooling device. The envelope is disposed about a longitudinal axis, and has a penetration disposed laterally, relative to the longitudinal axis. The valve is disposed within the one or more penetrations and has a closed position and an open position. The instrument is operable for the sensing of the fluid properties, and has a probe disposed in contact with the fluid through the valve in the open position.