HOWTO: Activate SSH in your existing sandbox
SSH credentials are visible inside the WP Sandbox dashboard. Here's how to get started with SSH for any of your sandboxes.
When you click into the details of any sandbox in the dashboard, you'll see a button that says "Activate SSH." Click that, and your credentials will be generated.
You can regenerate (roll) these credentials any time you'd like to change the passwords (for the sake of security, perhaps). Feel free to deactivate SSH at any time.
If you've enabled the "Allow SSH access" option for a sandbox or template, your visitors will be able to SSH credentials in their WordPress admin in the WP Sandbox menu item.
Once you generate SSH credentials for a sandbox (from the dashboard), you should use those same SSH credentials for SFTP. Use port 22 for SFTP.