when the piston is pushed against caliper the fluid is compressed. and when the piston is released there is a fluid bubble in the resivor. take the cover off your resivor and have some one push the brake and watch the motion of the liquid. however slight there is circulation. now just use your turkey baster and change your fluid. brake fluid is very cheap so who cares about waisting brake fluid. My car is 24 years old and the brake fluid has never been changed even with the turkey baister... I will change tomorrow with the turkey baister and report back to you the color change... right now it looks like mudd.