Sounds like your Lexus ES300 failed the LPFET (Low Pressure Fuel Evaporative Test). The Low Pressure Fuel Evaporative Test (also known as the EVAP test) ensures that there are no leaks in-between the hose leading from the Gas Tank to Charcoal Canister, or anywhere raw fuel (gasoline) may leak, either in liquid form or fume.
During the LPFET the smog technician clamps the end of the fuel vapor hose leading to the charcoal canister and pressurizes the gas tank with Nitrous Oxide via the LPFET test tool. The tool will then measure and calculate the drop in pressure due to any leaks. Technically there should be very little drop in pressure once the EVAP system (gas tank) is pressurized.
If in fact your Lexus ES300 has a leak somewhere in EVAP system it will be necessary to locate the leak and repair it prior to being able to pass the LPFET. Depending on where the leak is located, this repair may be cheap or expensive. The first step however is to find the leak. Look for brittle, broken, loose, and/or disconnected fuel vapor lines. Be sure not to confuse fuel pressure lines with vapor hose. Pressure lines deliver fuel only. Vapor line transfer and store fuel tank vapors to the charcoal canister and then vent them to your Lexus' intake manifold.