"To empty the breast" is an expression referring to a baby or child sucking milk from a mother's breast until it is fully fed or the milk supply is used up. Full definition
Make sure that you completely empty your breasts at the sessions before and after the session that you're dropping. (exclusivepumping.com)
As these pumps generally don't empty breasts as well as their electric counterparts, manual pumps are generally the pumps of choice for women who only need to pump occasionally. (pregnancymagazine.com)
This will help baby empty the breast more efficiently. (healthlinksbc.org)