The first time I ever bought a WL yeast the guy warned me to open it slowly "like a warm bottle of shaken soda" so that it wouldn't gush.
Consider the pressure proof that the yeast is viable. And losing some is not an issue at all since you are doing a starter.
On Tap: 1. Kelly R. IPA, 2. Roter Hund Hefeweizen, 3. Bud Killer Blonde, 4. Red Dog Pale, 5. Roter Hund Oktoberfest, 6. Pumpkin Ale, 7. McRed's Stout (with new nitro system and stout tap,) Cream Soda, 8. ESB # 3, & 9. Ordinary Bitter.