Custom URL Rewrites

I have links in my site that pass queries to pages that query from an external database. This works fine e.g.

http://www.mysite.com/catalog/?tl=flooring

however i want to rewrite this url to appear as

http://www.mysite.com/catalog/flooring

Ive tried modifying the rewrite rules in wordpress but it always displays the index page
[code]
add_filter('rewrite_rules_array','wp_insertMyRewriteRules');
add_filter('query_vars','wp_insertMyRewriteQueryVars');
add_filter('init','flushRules');

// Remember to flush_rules() when adding rules
function flushRules(){
global $wp_rewrite;
$wp_rewrite->flush_rules();
}

// Adding a new rule
function wp_insertMyRewriteRules($rules)
{
$newrules = array();
$newrules['(catalog)/([a-zA-Z0-9 ]+)$'] = '/catalog/?tl=$matches[2]';
return $newrules + $rules;
}

// Adding the id var so that WP recognizes it
function wp_insertMyRewriteQueryVars($vars)
{
array_push($vars, 'id');
return $vars;
}
[/code]