Appreciate your comments TechII,
I figure I can do a vacuum test on the lines and also check the purge valve to ensure it closes/seals properly.
I wanted to understand that mess under the car which is part of the purge canister and vent valve setup. That's why I requested the diagram.
I'll start with the easiest and most likely culprits and work from there.
I agree if I can't find it via the basic testing, smoke testing will probably be the only way to nail it.
Thanks