How to get drush working with a private mysql instance

I am looking for advice on getting drush to work with a private mysql instance.

All drush commands seem to work on my regular databases. But starting a drush command from within a drupal installation working with a private mysql instance leads to the following error message:

Drush was not able to start bootstrap) the Drupal database. [error] Hint: This may occur when Drush is trying to:

• bootstrap a site that has not been installed or does not have a configured database. In this case you can select another site with a working database setup by specifying the URI to use with the --uri parameter on the command line. See drush topic docs-aliases for details.
• connect the database through a socket. The socket file may be wrong or the php-cli may have no access to it in a jailed shell. See http://drupal.org/node/1428638 for details.

Database is addressed in settings.php with the following lines:

$databases['default']['default'] = array( 'driver' => 'mysql', 'database' => 'xxrecht', 'username' => 'xxrecht', 'password' => '...', 'host' => '159.xxx.151.15:29xx2', );

Any advice would be welcome.

Thanks,

Eric