From Dan Campeau...
When you milk it out,,, if it still looks white I would continue to let largest pup milk it out every 4 hours to make sure you are releasing pressure and it will usually work itself out.
If the milk looks yellow or green or has blood in it then I would get a breast pump, milk the teat out several (4-5) times per day, put your bitch on amoxycilline for 2 weeks and tape it so pups cannot nurse from it. While bitch is on antibiotics I give pups 1-2 cc of vanilla yogurt everyday so they do not loose their beneficial gut bacteria.
*** When the milk goes back to white with no signs of blood then I would put bigger pups on it to to keep it milked out.
I usually feel the bitches underline every 4-6 hours when I bring mom back in from being outside to exercise,,, and if one teat starts feeling hard or hot I get the biggest pups to milk it out for next couple of feeding cycles and it usually will clear up on its own.