The $dirty_html is a string, or an array of strings, proberly you have create a array of you're data with the name $dirty_html.
<?php
require_once 'htmlpurifier/library/HTMLPurifier.auto.php';
$dirty_html = array('seconds' => $_POST['seconds'], 'kills' => $_POST['kills'],'deaths' =>$_POST['deaths'],'wave' => $_POST['wave'],
'score' => $_POST['score'],'name' => mysql_real_escape_string($_POST['name']),'hash' => $_POST['hash'],
'date' => $_POST['date'],'time' => $_POST['time'], 'timezone' => $_POST['timezone'], 'userdata' => $_POST['userdata'],
display => $_POST['display']);
$config = HTMLPurifier_Config::createDefault();
$purifier = new HTMLPurifier($config);
$clean_html = $purifier->purify($dirty_html);
print_r($clean_html);
?>
Note i've not tested the code.