Using smoke to detect a vacuum leak

I was thinking about trying to make a home made smoke machine thing to find vacuum leaks. Or blow cigar smoke into a tube or something. Anyway, what hose do I remove to blow the smoke into? and is the whole system connected? Can I just blow it in any vacuum line?

Propane torch, turn on the propane (unlit) and move it around all the vacuum lines, the engine will speed up when it draws in the propane and you have found your leak.