Sipp's agent, Hunter Bledsoe, said he could earn up to $700,000 with incentives.
The 30-year-old comes to the Astros with a career 3.84 ERA in 304 appearances with the Indians (2009-12) and the D-backs last season. He's held lefties to a .224 average in his career and righties to a .209 mark.
"It's definitely kind of a better chance coming to a club searching for some kind of stability and me just, not trying to make a name for myself, but to almost prove to yourself that you still have the same success that you had the last few years," Sipp said. "I had a down year last year, and to get an opportunity to go out there and prove yourself, prove to everyone else that this is where you belong, that's what every player wants. I want to make a home, and there's no better place than Houston."
Astros general manager Jeff Luhnow said Sipp was added to fortify the bullpen, as well as giving manager Bo Porter another left-handed option to join Raul Valdes. Luhnow said the Astros had good reports from Sipp during Spring Training and saw improved control this year, and they like he had success against right-handers and left-handers.
"It gives Bo a lot more flexibility to have two left-handed options in the bullpen," Luhnow said. "I think Valdes has done a nice job, but Bo had to think carefully about when to use that bullet each game, and now he has two options."
Sipp will provide help to an Astros bullpen that ranks last in the Majors in ERA at 5.86 and is tied for the most blown saves with six. Kevin Chapman began the year as the lefty specialist, but was optioned to Triple-A after giving up five runs and five hits in 3 2/3 innings.
Sipp joins fellow veterans Chad Qualls and Matt Albers in the bullpen, though Albers is on the disabled list.
"Just like anything, you want to sit back and get acquainted with the guys before I start giving my input," Sipp said on whether he'll serve a leadership role to the young pitchers.
Clemens, 26, has made four appearances for the Astros this season, posting a 4.73 ERA. He pitched on Wednesday against Washington, tossing 3 1/3 innings, while allowing one run.
Crain, 32, has been on the disabled list the entire season while recovering from offseason surgery on his right biceps. He currently is rehabbing at the Astros Spring Training complex in Florida, throwing off flat ground, after being diagnosed with bursitis last week.