Annoying tmp files on shared host

I host a site on a shared server that, recently, is constantly sending 
me emails about running out of space. This account is a small (100MB) 
account, and when I go into cPanel and look at the disk usage, 
/tmp/urchin is usually the culprit (most of the time > 75MB).
I cleared them out Wed, and by yesterday it was full again.

I was going to complain to my host about it, but then I realized I 
wasn't sure how those were supposed to be cleared out.
I wasn't sure if they were supposed to auto-magically evaporate, or if I 
should setup a cron job or something. I've never run into this before so 
I was hoping one of you might be able to shine some light on it.

-- 
Chris Martin
Web Developer
Open Source & Web Standards Advocate
http://www.chriscodes.com/