How can I create an alias that goes to /dev/null?

Part of my old catch-all solution was to forward known-spammy email addresses to /dev/null. So what I would do is signup at spammysite.com with spammysite@mydomain.com, and when they sell the email to lists, it would automatically blacklist spammysite@medomain.com email to /dev/null.

I found this, but its not what I want (I don't even want to waste spam processing on it):
Talk:How to create a /dev/null account or spam trap? - Zimbra :: Wiki