If milk has backed into your Freemie Pump discontinue use. Replace the pump or use another back up method for expression. To avoid risk to health or injury, DO NOT attempt to use or repair the damaged pump. 

If milk has only backed into the tubing but not the pump, review this article about milk in tubing.

If you are unsure if milk went into the pump caution is urged. Inspect the pump tubing port for any dried or milk residue. Smell the pump for spoiled milk odor. Inspect the tubing to see how far down the line the milk passed. If it did not pass the Y-connector, your pump is probably not damaged. If it reached the pump tubing port continued use is not recommended. 

When used as directed, milk will not back up into the pump. Misuse is not covered by the limited warranty. Cup barriers protect the tubing and pump from milk back flow and if damaged can cause pump failure. Cup parts should always be correctly assembled and inspected before and after each pump session. 

Note: Use of Freemie Pumps with incompatible Freemie 1st generation Original System Collection Cup parts can damage your pump. Do not use portable Freemie Pumps with cups that use a valve base part that looks like this: