T.S.
Saturate the rust with lemon juice and sprinkle with salt, then lay it in the sun. If this doesn't work, re-apply lemon juice and salt and pour hot or boiling water through the stain, or as hot as the fabric will tolerate. Also try covering the stain with cream of tarter, then gather up the edges of the fabric and dip it in a bowl of hot water. Let it sit for 10 minutes and then wash as normal.