i am getting a lot of catch-all un rutable mail, that my hosting clietns accts. are getting full and not clearing out, i need to know how i can set it so it clears our that account automaticly.. i have it to blackhole new accounts but what abbout current accts.

You could tell your clients how to setup the blackhole in cpanel (sounds like what you are using) and then just have them do it themselves. If they want to not have their email fill up they will probably do it.