This hose is the return line from the compressor bypass valve (otherwise known as a blow-off valve) back to the turbo inlet. It's 99081 in the diagram. Includes hose and two clamps.
Fits all 2002-2007 Subaru WRX, 2004-2021 WRX STI, and 2006-2008 Forester XT. Does NOT fit 2004-2005 Forester XT -- that car uses THIS hose.