In the private areas (backoffice), there is no way to send all the spams into the trash in on click
But you can use phpmyadmin ou the SQL console to remove the spams
for instance :
DELETE FROM <span class="base64" title="PGNvZGUgY2xhc3M9InNwaXBfY29kZSBzcGlwX2NvZGVfaW5saW5lIiBkaXI9Imx0ciI+c3BpcF9mb3J1bTwvY29kZT4="></span> WHERE id_forum > 300 AND id_forum < 900
remove all the messages between message #300 and message #900
And
TRUNCATE TABLE <span class="base64" title="PGNvZGUgY2xhc3M9InNwaXBfY29kZSBzcGlwX2NvZGVfaW5saW5lIiBkaXI9Imx0ciI+c3BpcF9mb3J1bTwvY29kZT4="></span>
remove all the messages (be careful !)