Basically you pull from a repository that your clone is made from. But what if I want to pull from a different repository, as you would do with this command:
hg pull REPO_URL
How is this done in TortoiseHG?
Did you try to read hgrc for repo?
In it's [paths] section you can define as many paths to repo as you want by hand, or add additional repos with GUI in Synchronize tool and later use the Synchronize for selecting needed external and pull-push with it