Two /tmp directories, both full. Please help

Dear users,

Today, I have received a warning from my server. Both /tmp directories are (almost) full. I've listed both locations below.

Current Disk Usage

/dev/mapper/vg_cpanel-lv_root
tmpfs (1.9 GB space, 70M left, located in: /var/tmp)
/dev/vda1
/dev/mapper/vg_cpanel-lv_tmp (1.5 space, 0M left, located in: /tmp)

I've configured a cronjob to clean tmpfs every 6 hours. However, I'm not sure if I can clean /dev/mapper/vg_cpanel-lv_tmp too. Any ideas? Thank you very much.

Edit: p.s. I'm experience heavy issues with the server. Users cannot login to their website (e.g. Wordpress systems). This is critical.

Edit 2: fingers crossed, I have cleaned /dev/mapper/vg_cpanel-lv_tmp. Let see if that works. It seems all user sessions are stored in this tmp.

Edit 3: hell yeah, it works! :D All users can login to their website again.

Main question for now: how does my server clean /dev/mapper/vg_cpanel-lv_tmp each 6 hours itself? This cronjob will obviously not work: 0 */4 * * * /usr/sbin/tmpwatch -am 12 /tmp > /dev/null 2>&1

Edit 4: I've written this cronjob in order to make /tmp clean for files older than 3 days: find /tmp -mtime +3 -delete

Or should I use -rm instead?