Begin by ensuring that you have access to a PostgreSQL database and that your Google Cloud Platform (GCP) project is set up. You will need to have the Google Cloud SDK installed and configured on your local machine. Also, ensure you have the necessary permissions to interact with both PostgreSQL and Google Pub/Sub.

Navigate to the Google Cloud Console, go to the Pub/Sub section, and create a new topic. This topic will serve as the destination for the data you are moving from PostgreSQL. Make sure to note down the topic name as you will need it in subsequent steps.

Install the necessary Python libraries to interact with PostgreSQL and Google Pub/Sub. Use the following command to install:
```
pip install psycopg2 google-cloud-pubsub
```
`psycopg2` is used for connecting to PostgreSQL databases, and `google-cloud-pubsub` is used for interacting with Google Pub/Sub.

Write a Python script to connect to your PostgreSQL database and extract the data you need to publish. Use `psycopg2` to establish a connection and execute SQL queries. Here is a basic example:
```python
import psycopg2

conn = psycopg2.connect("dbname=your_db user=your_user password=your_pass host=your_host")
cur = conn.cursor()
cur.execute("SELECT FROM your_table")
rows = cur.fetchall()
cur.close()
conn.close()
```

Depending on the structure of your data and the requirements of your Pub/Sub topic, you may need to transform the data. This could involve converting the data into a JSON format or any other format compatible with Pub/Sub messages.

Use the `google-cloud-pubsub` library to publish the data to your Pub/Sub topic. Here is a basic example of how to publish messages:
```python
from google.cloud import pubsub_v1

publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path('your-project-id', 'your-topic-name')

for row in rows:
data = str(row).encode('utf-8') # Convert row to bytes
future = publisher.publish(topic_path, data)
print(f'Published message id: {future.result()}')
```

After publishing the data, verify that it has been correctly transmitted to Google Pub/Sub. You can do this by checking the Pub/Sub topic for messages or by setting up a subscriber to receive messages from the topic and logging them for verification.

By following these steps, you can move data from PostgreSQL to Google Pub/Sub without relying on any third-party connectors or integrations. Ensure that you handle any exceptions and manage connections appropriately for production-level code.