Completely empty page
You can do that through a custom module - create a path and instead of returning the output, just print it.

Here's an example:

/**
 * Implements hook_menu().
 */
function YOURMODULE_menu() {
  $items = array();
  $items['custom-url'] = array(
    'page callback' =&gt; 'YOURMODULE_blank_page_callback',
    'page arguments' =&gt; array(),
    'access arguments' =&gt; array('access content'),
    'type' =&gt; MENU_CALLBACK,
  );
  return $items;
}

/**
 * Display the content for your blank page.
 */
function YOURMODULE_blank_page_callback() {
  print 'Your string.';
}