When you “pump and dump,” you pump breast milk from your breasts and throw it away rather than saving it for baby (usually dumping it down a drain). Some women mistakenly believe they must pump and dump to help remove alcohol from their breast milk after having a drink, but this is actually a myth. Alcohol leaves your breast milk just as it leaves your bloodstream. Pumping and dumping doesn't “get rid of” the tainted milk — time does.
So when should you pump and dump? You might want to if you’ll be away from baby during one or more feeding times, and there’s no practical way to carry your milk along. (Your milk is good for six to 10 hours at room temperature assuming the temp is less than 80 degrees F, so this is seldom an issue.) Or, if you have reason to believe there is temporarily something in your milk that is harmful to baby (like alcohol or other drugs) you may need to pump and dump at feeding times (and feed baby previously pumped breast milk instead) until enough time has passed for the substance to be out of your system. In most cases — like with alcohol — you aren't pumping to remove the “bad” milk. You're pumping to maintain your supply and prevent engorgement while you wait for the bad stuff to leave your body.