I had to respond to this one.  Yes there some milk in the breasts at all
times in a lactating mother but it is minimal.  The analogy I use with my
mothers is that you make milk (not exactly but close enough for lay
understanding) like you make tears.  You don't have little balloons full of
"water" under your eyes waiting to cry.  Your body creates them at need.  So
when your body is stimulated to make milk it uses the material on hand at the
moment (blood) and so whatever the level of whatever is there at that time is
what needs to concern you.  Hence the advice given to mothers that if they
want an alcoholic beverage, breastfeed first then have your drink and in a
couple of hours the level is way down.

Sharon Coe LPN IBCLC