A breast pump system includes a fluid isolator that is particularly useful as an aftermarket product that can be readily installed between various vacuum pumps and milk collection devices. The fluid isolator includes a pliable, limp diaphragm that equalizes the pressure between a vacuum pump and a milk collection device while providing a barrier that prevents milk from accidentally backflowing from the milk collection device to the vacuum pump. In some examples, the fluid isolator includes one or more tiny supplementary openings for synchronizing the movement of the diaphragm with the cyclical action of the vacuum pump and/or for returning a misdirected milk droplet in a suction tube back to a charging chamber of the milk collection device.
