Oh, I looked into this. It's one of the myths perpetrated by their propaganda.
Many North Koreans believe that Kim Jong-il did not use the toilet.True or False?: True
North Korea engages in a "cult of personality"—the Kim family's members have been elevated to the level of deities. To reinforce this status, official North Korean media attributes incredible feats to the family. For example, there's the oft-cited anecdote that Kim Jong-il never used the bathroom. And as insane as that sounds, this was a well-established "fact" in North Korea, and multiple defectors have corroborated this story.
Jang Jin-sung, a defector who was once a propaganda poet for Kim Jong-il, admitted in interviews that he believed the bathroom story into adulthood. It was only when he met Kim Jong-il, face-to-face, that he realized it was not true.
source: http://www.complex.com/pop-culture/2014/12/crazy-stories-about-north-korea-kim-jong-un/bathroom