We are trying to deindex a large quantity of pages on our site and want to know what the best practice for doing that is. For reference, the reason we are looking for methods that could help us speed it up is we have about 500,000 URLs that we want deindexed because of mis-formatted HTML code and google indexed them much faster than it is taking to unindex them unfortunately. We don't want to risk clogging up our limited crawl log/budget by submitting a sitemap of URLs that have "noindex" on them as a hack for deindexing. Although theoretically that should work, we are looking for white hat methods that are faster than "being patient and waiting it out", since that would likely take months if not years with Google's current crawl rate of our site.