The guy who services my machine told me the following: With the presser foot up, the tension disks are not together, so you can pull the thread in either direction without doing any harm. If the presser foot is down, then you should only pull the thread through the needle end, because it's not good for the tension disks to have the thread go through them in the wrong direction. I'm not sure it would be good for the tension disks to have a knot go through them either, but that's just speculation on my part--it might clean lint out and be helpful, as some of you suggest.