The problem I have, when using balls caged from the next door driving range, is that the chopped up balls get stuck in the hose. Darn'd if I'm going to use a new Titlist.
Seriously... Try zipping the bags all the way shut, and then, pinch the zipper about a half inch from the end and opening that last half inch. Press the end of the zipper against your "pinched" spot, which opens up a small "blow" (suck) hole. When you have sucked the air out of the bag, keep sucking while you slide your "pinch" to seal the zipper.
Don't know about 6 months, but it keeps the bags flat while I stuff them into the stuff sack. All I'm trying to do is reduce volume for packing.