Hello,
If fuel level sensors have serial (RS232/RS485) interface you can connect sensor to the router, and then configure router to work in Over IP mode (more information here ). In such configuration router will work as Serial/IP gateway, allowing sensor to send information to remote server.
If fuel level sensor supports ModbusTCP or ModbusRTU protocol you can configure router to work as Modbus TCP Master or Modbus RTU Master (more information here), which will allow router to request data from the sensor and if needed to transfer collected data to remote server.