Drupal 6 module to delete old unapproved comments.

clean_comments.info

name = Clean Comments
description = "Remove old unpublished comments"
core = 6.x
dependencies[] = comment

clean_comments.module

<?php
define('DEFAULT_CLEAN_COMMENTS_SIZE', '1000');
define('DEFAULT_CLEAN_COMMENTS_MIN_DAYS', '30');

/**
 * Implements hook_menu().
 */
function clean_comments_menu() {
  $items = array();

  $items['admin/settings/clean_comments'] = array(
    'title' => 'Clean comments',
    'description' => 'Configure comments cleaning',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('clean_comments_admin_settings'),
    'access arguments' => array('administer clean comments'),
    'type' => MENU_NORMAL_ITEM,
  );

  return $items;
}

/**
 * Form builder; Global settings form.
 */
function clean_comments_admin_settings(&$form_state) {
  $form['clean_comments_size'] = array(
    '#type' => 'textfield',
    '#title' => t("Number of comments to clean per cron run"),
    '#default_value' => variable_get('clean_comments_size', DEFAULT_CLEAN_COMMENTS_SIZE),
  );

  $form['clean_comments_min_days'] = array(
    '#type' => 'textfield',
    '#title' => t("Comment minimum age"),
    '#description' => t('Only delete unpublished comments older than this number of days'),
    '#default_value' => variable_get('clean_comments_size', DEFAULT_CLEAN_COMMENTS_MIN_DAYS),
  );

  return system_settings_form($form);
}

/**
 * Implementation of hook_cron().
 */
function clean_comments_cron() {
  module_load_include('inc', 'comment', 'comment.admin');

  // Find out the comment ids of the comments that are unpublished
  // and are older than X days.
  $min_age = strtotime('today - ' . variable_get('clean_comments_min_days', DEFAULT_CLEAN_COMMENTS_MIN_DAYS) . 'days');
  $result = db_query('SELECT c.*, u.name AS registered_name FROM {comments} c INNER JOIN {users} u USING(uid) WHERE c.status = 0 AND c.timestamp < %d LIMIT %d',
        $min_age, variable_get('clean_comments_size', DEFAULT_CLEAN_COMMENTS_SIZE));

  if ($result) {
    while (($comment = db_fetch_object($result)) !== false) {
      $comment->name = $comment->uid ? $comment->registered_name : $comment->name;
      _comment_delete_thread($comment);
      _comment_update_node_statistics($comment->nid);
    }
  }
}