From my experience,
1. If you are talking about the seal n'go type, you cannot connect them directly to the Medela pump.
2. Normally, milk will be poured out through the edge of the bag, so not much milk will pour through the part above the zipper. Even though you are not careful (that's me), I think it is not a great concern (as in my case, my baby is so far so good...). But I change to use bottle to store eventually because of bettle handling and much convenience...
Thank you for your advice. I am now using the bottles for freezing but problems might arise after I go back to work - cos I need to work overnight and I estimate that I need to bring 10 bottles ! What I am thinking of is trying to connect the milk bags to the pump with a iron strip (like the one for closing the gabbage bags; I am trying to simulate the Medela milk bags) but I doubt whether it works.
So I may try to pump out the milk into a sterilized bottle and then pour into the bag for storage.
so you let them freezed first in the upright position before you lie it flat, or the zipper is safe enough to let it flat when it is full of liquid milk inside?
also I found that there is a 'Gerber disposable bottle' specially designed for using the Gerber milk bags. but I don't know how to use it, and also not sure if it is really necessary.