ALWAYS remove the fill plug first, that way if you can't get the plug off then you haven't drained the fluid first. Also, the way I do it is remove the fill plug and remove the reverse sensor, then remove the drain plug and drain all the fluid, then install plug and fill with a funnel through the reverse sensor hole. Then we it comes out of the fill hole cap it off. then reinstall the reverse sensor your done. Pretty damn easy job.