This is a fair question. But your previous users' answer was incorrect. The easy way to remember which is what; IS: Cylinder one in in bank one. Cylinder two is in bank two. For the engine codes lised below. So says Toyota..
This service bulletin provides information on the proper identification of engine bank 1 and engine bank 2 for correct A/F sensor and oxygen sensor replacement. This bulletin contains information that identifies engine bank 1 and engine bank 2 on the following engines: 1AZ-FE, 2AZ-FE, 2AZ-FE (PZEV), 1GR-FE, 2GR-FE, 2GR-FSE, 2JZ-GE, 1MZ-FE, 3MZ-FE, 1UR-FSE, 3UR-FE, 2UZ-FE, 3UZ-FE, 5VZ-FE, and 1ZZ-FE.
• Bank 1 (B1) refers to the bank that includes cylinder No. 1.
• Bank 2 (B2) refers to the bank opposite bank 1.
• Sensor 1 (S1) refers to the sensor that is located before the catalytic converters.
• Sensor 2 (S2) refers to the sensor that is located after the catalytic converters.