two codes corolla

My son came home from college and brought with him two check engine codes!

2005 corolla...80,000 miles. The car runs fine but we have a po455 and a po461 code according to advance auto. Any suggestions!

P0455 - Evap system failure (Gross leak / No flow)
P0461 - Fuel level sensor failure

Can you smell fuel?
Is the Gas cap on tight?

The EVAP system keeps control of fuel emissions.

Thanks for the advice. I will start from scratch and tighten the gas cap and see what happens. I disconnected the battery and removed the codes. Is that the correct way? How long before the codes come back if that was not the problem? Thanks Again!