anyone with experience with Fog Machine Test for EVAP

hi I working on a 2000 gmc Sonoma

I cant find the small leak.... I using a fog machine to pump fog into the gas tank I made an adapter it pumps it in but I have it disconnected at the purge valve at the front of truck

but I don't see smoke come out of the line... do I need to have truck running

how do I get this smoke test to work first time doing it figured all u do is plug in and goooo