Ten Thousand Dream Interpretation

by Gustavus Hindman Miller
Drinking buttermilk, denotes sorrow will follow some worldly pleasure, and some imprudence will impair the general health of the dreamer.

To give it away, or feed it to pigs, is bad still.

To dream that you are drinking buttermilk made into oyster soup, denotes that you will be called on to do some very repulsive thing, and ill luck will confront you. There are quarrels brewing and friendships threatened.

If you awaken while you are drinking it, by discreet maneuvering you may effect a pleasant understanding of disagreements.

The Complete Guide to Interpreting Your Dreams

by Stearn Robinson - Tom Corbett
If you drank it, you will be worried by some past indiscretion, but the difficulty will soon pass.

If you threw it out, or gave it away, you must avoid hasty decisions (or actions) regarding matters of importance.

Mystic Dream Book

by Internet Archive - Anonymous
To drink it indicates disappointment in love.

To the married, trouble, sorrow and losses.