I am receiving some useless mails every now and then. I have applied a filter for it in my Inbox in Gmail, but it resides in Trash. I also want it to get deleted instantly as it comes into Trash as well.
Please suggest me an automated functionality to do this.
You can't do that from the web app, it gets emptied automatically after 30 days. You could do it via IMAP, from a desktop client.