pour back (in(to))
To return some liquid to its previous receptacle. A noun or pronoun can be used between "pour" and "back." You've already started drinking that soda—you can't just pour it back now! If you don't want the water, just pour it back in the sink. I poured back the cooking oil into the bottle to use it again another day.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
pour something back (in)and pour something back into something
to replace a liquid into something. Larry poured the extra glass of orange juice back into the pitcher. Lily took too much and poured some back. Pour back the extra juice into the pitcher.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.