Trash as in Deleted Items? Right click on the folder and Empty Deleted
Items.
If you're speaking of other folders:
To delete all: Highlight one and Ctrl + A will highlight them all. -
Delete.
To delete a section: Highlight the first one you want to delete. Scroll
down to the last one and click on it while holding the Shift key down. -
Delete.
To delete multiple messages that are interspersed: Hold down the Ctrl key
while you click on each message to highlight. - Delete.
Also: Shift + Delete will bypass Deleted Items.
