Drainage from your breast
is not considered mucus in my experience but perhaps your surgeon was simply trying to illustrate what the material was like. Wounds often do separate after reductions and will grow bacteria when cultured. Red along the edges of the wound is normal too. But spreading redness, fevers, increasing pain, etc are not and those signs require you see your surgeon. Often there is yellow slimy tissue in the wound that that is simply dead skin that will have to slough or be removed for the wound to heal. So continue to trust your surgeon and follow the instructions given to you by him/her.