Originally Posted by cyccommute

You probably aren't leaking from the bottom but are leaking from the top. The most likely spot is the bag's "cap". Either it isn't on properly or an o-ring has deteriorated. Fill the bag, turn it upside down, and squeeze it a little. You'll see where the leak is coming from.

I've had many, many bag and never had one leak from anywhere but the cap. The edge seams are sealed very well and are almost never a problem.