The Astros whittled down their roster to a season-opening 25 on Wednesday with a series of moves that included placing righthanded pitcher Henry Sosa on waivers. Sosa, 26, cleared waivers and accepted an assignment to Class AAA Oklahoma City, where he will pitch in the starting rotation. The team also purchased the contract of Travis Buck, who will serve as a fourth outfielder, assigned fellow outfielder Justin Ruggiano to Oklahoma City and placed lefthanded pitcher Sergio Escalona (elbow) on the 15-day disabled list.