"Backflow protectors" are devices used to prevent the reverse flow of substances, such as liquids or gases, back into a system or pipe. Full definition
The majority of personal grade pumps on the market today use backflow protectors — the same technology that hospital grade breast pumps use to make them safe for multiple users — so as a buyer you have a lot of freedom regarding things to consider when buying a breast pump, even when buying a used breast pump. (pumpables.co)
You insert the smaller end into the Medela breastshield (it's the same shape as the Medela tubing connector) and the other end will have the Spectra backflow protector fitted into it. (pumpables.co)
This means the pump kit includes some sort of backflow protector (the UFO - looking things on the tube) or filter between the parts that touch milk and the pump itself. (pumpables.co)