"You have to be able to see the air, can you... lol"
LOL
Have you seen them smoke machines that the dealer us to find EVAP leaks?
When i us to work at the chry dealership, i alway wanted to take that machine home and us it on my flow bench(I actually did once...)
For those that don't know what this is, it a smoke machine that seals to your fuel tank neck. Were ever the fuel vapors are leaking it leave a trace of dye behind that you can see with a black light.