The CDC recommends taking the pump completely apart (if applicable) and thoroughly rinsing each individual piece. If your breast pump is dishwasher friendly, then you can pop it in there. If it isn't, you can wash it by hand using hot soapy water. If you’re hand-washing, make sure you’re using a brush that you only use for cleaning bottles, then rinse the pieces again and let them air dry. To further sterilize it, you can place the pump in a pot of boiling water for five minutes before letting it air dry (however, check your pump manufacturer’s guide before you do this).