2000 sable/tauris p s pump

What is that pipe with that black oval canister leading to the power steering pump. I have a strange growling noise in my engine when I accelerate and want to try replacing the p s pump because when I removed the belt the pump shaft moved back and forth. Are they supposed to do that?.

its the high pressure line, it goes from the pump to the rack. Its expensive and a bitch to replace, and no, the pulley shouldn't have any shaft play.