I just use value bleach, a few drops on the stain neat then rinse well in cold water and then wash it normally. If you don't rinse it properly you may ended up bleaching other clothes that it touches in the wash IYSWIM.
I soak the stained clothes in bowl of water with borax. Borax is cheap. It never fails. Also have old fashioned bar of Fairy Laundry soap which is good on dirty collars. The Fairy soap lasts forever!!!!