Like Heinek said... you pump that baby full of smoke and see where it comes out. Use a gascap adaptor...
Then if that all checks out you pull off the main charcoal cannister hose and pump into there with the real gascap on to make sure it doesn't leak there either.
Anywho... it's all lines run under the car.. usually a 3rd line is along with the 2 liquid fuel lines. Charcoal cannister can be under the rear bumper.. under a headlight.. or mounted near the fuel tank.. dunno exactly where it is on the Alero.
Honestly diagnosing yourself without a smoke machine is almost impossible.
But, either way... an EVAP code WONT WONT WONT cause lower gas mileage. The only reason I would throw money at this problem is to pass registration inspection... or if you're anal about the SES light.