Can be used in many pumps including Ameda Mya Joy (note not for May pro or Mya) Ameda Purely Yours, Lansinoh Double Electric Pumps etc.
It is OK to see a small gap (less than 0.5mm) between the lips of the duckbill when not in use.
It is not a defect. It can close properly during a pump action.
Wash this piece with hot, soapy water. It is not advisable to insert any object into the valve opening to clean it.
This may tear or stretch the part resulting in poor performance.