How do I empty the trash folder in my pop email?

[AC Question]

I have the mail app set up for 2 different pop email accounts. Both are synced and set to delete on server when deleted on phone. Now I see my email trash folders still have the hundreds of emails I deleted. I am unable to find the option to Empty Trash or Select All and Delete. Please advise - very frustrated and don't want to use valuable storage on deleted emails.