1970 250/Rochester Monojet vacuum line question

[Love 70 Chevys]

Just got done rebuilding my carb and I want to put everything back together factory-like. What is this? (Arrow in first picture). The input line is from the vacuum advance on the distributor. The output line goes to the carb. Does it connect to the vacuum break (upper arrow in the second picture) or near the throttle adjustment screw (lower arrow in the second picture.) Any hints on how to test it to see if it still works? Thanks!