Is this what you mean?
11 0 1 * * /var/spool/cron/UM/cleanlogs 4000 1>/dev/null 2>/dev/null
The 1>/dev/null redirects stdout to /dev/null
The 2>/dev/null redirects stderr to /dev/null
Otherwise these are mailed to the owner of the cronjob. The use of them is simply to avoid potentially unecessary mail messages.
Note that redirection is actually part of the bash shell, so do a "man bash" to find out more.