Failed smog test fuel tank not holding vacum

I was going to say the same. After the test I'd drop the tank and get it cleaned out. There's got to be a lot of junk drifting around in there including the remains from the old float and who knows what from his hack job. Most radiator shops will do a great job. I dropped my tank because it had been sitting for eight years to get it cleaned out and could hear stuff rolling around inside and it was an old lady's car. Also looks like you need to wire brush the contact area on the tube where the ground clamps on.

Good luck on the test!