There is no option in the Gmail app to delete emails from the Trash folder, but you can empty the Trash folder directly from the Gmail website using either the Browser or Chrome apps.
Follow these steps to empty the Trash folder from the Gmail website.
- On the desktop, tap the Home icon.
- In the upper-right corner of the desktop home screen, tap the Apps & Widgets icon.
- In the Apps & Widgets screen, tap either the Browser or Chrome icon.
- In the Browser or Chrome screen, in the upper-right corner, tap the menu icon and then tap Request desktop site.
- Browse to https://mail.google.com/ and sign in to your Gmail account.
- At the Gmail website, scroll down and tap the Trash folder.
- In the Trash folder, tap to place a check next to all the messages you want to delete and then tap the Delete forever button.
NOTE: You can also delete files individually by tapping the Trash Can icon next to each message you want to delete.
- The Gmail application will update and, in the Trash folder, the deleted emails should be gone.