As an SEO, it is important to ensure that your website is free from error pages and empty pages. These types of pages can negatively impact your website's search engine rankings and user experience. Here are some steps you can take to remove error pages and empty pages from your website and prevent them from being visible on Google Webmaster:

1. Use a website crawler tool: A website crawler tool can help you identify error pages and empty pages on your website. Some popular website crawler tools include Screaming Frog, Sitebulb, and Ahrefs. These tools can crawl your website and provide you with a list of pages that return error codes (e.g. 404, 500, etc.) or contain no content.
2. Redirect error pages: If you have error pages on your website, you should redirect them to a relevant page using a 301 redirect. This will ensure that users and search engines are directed to a working page on your website instead of an error page. You can set up 301 redirects using a redirect plugin or through your website's .htaccess file.
3. Remove empty pages: If you have pages on your website that contain no content, you should remove them altogether. Empty pages provide no value to users or search engines and can negatively impact your website's search engine rankings. You can remove empty pages using your website's content management system (CMS) or by accessing your website's files directly.
4. Use the "Remove URLs" tool in Google Webmaster: If you have already removed error pages or empty pages from your website, you can use the "Remove URLs" tool in Google Webmaster to request that these pages be removed from Google's index. This will ensure that these pages are not visible on Google Webmaster or in search engine results pages (SERPs). You can access the "Remove URLs" tool under the "Index" tab in Google Webmaster.
5. Use the "Disallow" directive in robots.txt: If you want to prevent search engines from crawling certain pages on your website (including error pages or empty pages), you can use the "Disallow" directive in your website's robots.txt file. This will tell search engines not to crawl those pages. However, this method should be used with caution as it can also prevent search engines from crawling pages that you do want to appear in search results.