rewrite help for WPSE

wpse41778-rewrite.php

<?php
/*
Plugin Name: WPSE 41778 Rewrite
Author: Christopher Davis
Author URI: http://christopherdavis.me/
*/

add_action( 'init', 'wpse41778_add_rewrite' );
function wpse41778_add_rewrite()
{
    add_rewrite_tag('%gallery%','([^/]+)');
    add_rewrite_tag('%album%','([^/]+)');
    add_rewrite_rule(
        '^galleries/([^/]+)/?$', 
        'index.php?pagename=galleries&album=1&gallery=$matches[1]',
        'top'
    );
}

register_activation_hook( __FILE__, 'wpse41778_flush_rewrite' );
function wpse41778_flush_rewrite()
{
    wpse41778_add_rewrite();
    flush_rewrite_rules();
}