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IF did you do the work or someone else offered a hand doing it?

There should not be a hose in your hand if you did it. The tube looks to have a "check-valve" by the ways.

If the line was a vacuum line it would be making all kinds of fuss.

If it is the line or part of that line, your brake booster requires a check valve to operate.

 

I haven't had my base manifold in awhile but I remember there being a few vacuum lines that resemble that on the left side of the manifold for the IMRC and solenoid.