As FM said, it will all end up at the bottom.
Stab a few hundred holes in the bag with a fork, and slit a hole big enough to slip a hose into the top. Stand it in a bucket, and push the hose in the hole, and leave it for a few hours. Any sand that makes it out of the holes will land in the bottom of the bucket.
I've got to say though, having done a four foot with play sand, its really light. I've now capped it with a bag of the more expensive :FS aquaarium sand as its a more course grade and doesnt get blown about by the powerhead.