[brcidd]

In my 30 yrs of work- I have never seen or had a vacuum line that needed to be cleared- in most every case- it is a disconnect, a rub-thru, a burn thru, or a cracked line- or a check valve stuck shut- how would it even get plugged up?- also vacuum is the absence of air pressure- so it is measured in in-hg and can only go as low as what your barometer states is the current atmospheric pressure-

so I would trace the line from front of vehicle to the back and test at every junction, or splice for adequate vacuum- pretty easy actually- when I find the vacuum is missing- then back track to the leak--

NEVER pressurize a vacuum circuit- since vacuum lines do not use clamps, and only are pushed together at connections- you could blow the vacuum connections apart- in places you can't get to- and that is a real pain to fix.