I like to do easy things on my car myself. One of those being changing brake pads and shoes. While I have never done it on ABS equipped cars before I have heard that the brake fluid should be drained when pushing the brake cylinder back. I have always just pushed the cylinder back and pushing fluid back up into the reservoir. Why would the ABS sensors be "ruined" if the fluid is just pushed back up into the reservoir? I don't see how fluid flowing the opposite way for a short period of time would harm the sensor. To me that is like saying a multi-directional tire will be ruined if put on the other side of the car when the tire rotation is done. Any one know if this actually is bad for the ABS sensor? And if so explain why? Thank you.