Use antivirus.exim to delete SPAM emails

I'm trying to filter emails and send them to /dev/null when they are marked SPAM. below is a sample from the /etc/antivirus.exim file. logfile /var/log/filter.log if $header_subject: contains "SPAM" then logwrite "$tod_log $h_from $h_to $header_subject (the subject contains SPAM)" save /dev/null finish endif
I'm watching and see these messages get logged to /var/log/filter.log yet the messages end up in queue showing the From and To then eventually show up with bounce as the from. I would like to just have the filter remove these messages all together as my queue will eventually fill up with these messages. Anyone have a solution to this. I've been on the forums for days trying to get this to work properly. I've even put the save /dev/null before the logwrite.