Failed smog test fuel tank not holding vacum

amoparacer said

So I conclude that the vacuum finished off sending unit gasket or tank doughnut. Before the test i had no gas smell at all.

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Possibility. I'd fill the tank clear full and let it set in a cool area for 1/2 day or so and then look around under there for 'wet spots'. It's always possible something rusted through, and finally failed.