$db_server   = 'localhost';
$db_name     = 'testdb';
$db_username = 'drupaluser';
$db_password = '';

$db_server   = 'localhost:port';

$db_port = '33066';

{ $mysqli = new mysqli($db_server, $db_username, $db_password, $db_name, $db_port);
  ...