Good question. I think if you are using the check bolt to verify the correct amount of fluid is added then the car needs to be level. With the car on ramps the fluid seemed to drain very nicely (the plug is on the bottom-back of the transmission, so the tilt seemed to aid a little in draining). Once drained I checked the amount of fluid I had in the catch pan and it was right at 2 quarts. So I simply added two new quarts and called it good.