I have this script that collects data from users and I wanted to check their data for malicious code like XSS and SQL injections by using HTML Purifier http://htmlpurifier.org/ but how do I add it to my php form submission script?

Here is my HTML purifier code

 require_once '../../htmlpurifier/library/HTMLPurifier.auto.php';

 $config = HTMLPurifier_Config::createDefault();
 $config->set('Core.Encoding', 'UTF-8'); // replace with your encoding
 $config->set('HTML.Doctype', 'XHTML 1.0 Strict'); // replace with your doctype
 $purifier = new HTMLPurifier($config); 

 $clean_html = $purifier->purify($dirty_html);

Here is my PHP form submission code.

if (isset($_POST['submitted'])) { // Handle the form.

    $mysqli = mysqli_connect("localhost", "root", "", "sitename");
    $dbc = mysqli_query($mysqli,"SELECT users.*, profile.*
                                 FROM users 
                                 INNER JOIN contact_info ON contact_info.user_id = users.user_id 
                                 WHERE users.user_id=3");

    $about_me = mysqli_real_escape_string($mysqli, $_POST['about_me']);
    $interests = mysqli_real_escape_string($mysqli, $_POST['interests']);



if (mysqli_num_rows($dbc) == 0) {
        $mysqli = mysqli_connect("localhost", "root", "", "sitename");
        $dbc = mysqli_query($mysqli,"INSERT INTO profile (user_id, about_me, interests) 
                                     VALUES ('$user_id', '$about_me', '$interests')");
}



if ($dbc == TRUE) {
        $dbc = mysqli_query($mysqli,"UPDATE profile 
                                     SET about_me = '$about_me', interests = '$interests' 
                                     WHERE user_id = '$user_id'");

        echo '<p class="changes-saved">Your changes have been saved!</p>';
}


if (!$dbc) {
        // There was an error...do something about it here...
        print mysqli_error($mysqli);
        return;
}

}