1957 hudson power brake question

Unknown

allright, I got the gas return line fixed and drove the beast around brakes felt like they were there but no power assist. I put it on the lift and checked the power booster, the booster has a small junction plate with two tubes coming out of it a large and a small. the large has a hose on it that leads to a Y junction intersecting a vaccume canister and the manifold. The small tube which aims up has evidence of a line being on it (its clean) but no line is present, and there dosnt appear to be anything missing anywhere. can anyone tell me where this mystery line goes??