I need help with my Chinese Scooter?

okay my scooters is gravity feed meaning the carb is at the bottom and the tank is at the top. But I need some help the main gas line runs down to this 3 way valve. One line from the gas line, one line leads to the carb, and the last line I don't know where it goes and I need help! but the engine is a Geely D1E41QMB 2T its Chinese made that's all I know. I just want to plug the last line in to its rightful place. I think is a vacuum line. Thank you!