During pre-departure checks on an outboard fuel system, what must be done with the fuel tank air vent screw (tornillo de ventilación del estanque)?

1. Tighten it fully with a wrench to pressurize the tank to 50 PSI
2. Fill the vent screw with waterproof grease to seal it permanently
3. Remove the fuel hose and blow into the tank
4. Open the vent screw so atmospheric air can enter the tank as fuel is consumed, preventing engine-stopping vacuum lock