Medela Swing- ?

[grateful mama13]

I have a medela swing.. when I wash it I sometimes have a hard time getting the membrane( i think is what its called) off.. the little yellow part /w the flap on it. and when i go to pump i have no suction.. I don't know what i'm doing wrong here.. ? I'm almost positive it has something to do with that piece.. but it looks normal to me.. anyone else have this problem or know what im doing wrong?