Well, here are the definitions of the codes:
P0441 - Evaporative Emission Control System Incorrect Purge Flow
P0442 - Evaporative Emission Control System Leak Detected (small leak)
P0446 - Evaporative Emission Control Sytem Vent Control Circuit
Based on my experience, the problem is in the purge control circuit under the hood, and includes the line running from the charcoal canister to the engine, which happens to be the purge control line. To accurately determine the problem will require additional diagnostics. This can happen to any car. In my experience, Toyotas have not had any more problems with the evap system than any other make. Since your only solution so far has been to tighten the gas cap and reset the codes, you may need to find a real mechanic.