Basically I have so many images associated with custom post type that I need to be able to safely delete all related media on removal from trash.
Is there a safe way of doing this?
Is your post to image association custom?
If not attachments should be automatically deleted by Wordpess. If the connection is custom, Wordpress provides a delete_post action that fires before and after a post is deleted, it will pass the ID of the post so you can use that to delete all custom content associated with it.