I’ll be typing along, my characters are doing Semi-Important Story Stuff, and all of a sudden a random thought will strike me and I’ll stop dead. And that thought is: Are my readers going to wonder why none of these people ever seem to go to the bathroom?
I usually tell myself that of course they don’t, or that if they do it’s just a funny little passing wonder. . .until one day I was cruising around on Cracked.com – yes, I know, it’s a bad habit – and ran across a listicle nitpicking the Star Wars universe. I don’t have a problem with nitpicking per se, since it is one of the Five Springs of Inspiration which feed the Bottomless Lake of Fanfiction, but the very first entry on the list just happened to be about how we never see decent bathroom facilities in Star Wars and therefore the whole of Mos Eisley must be covered in shit.
I’ll just do a writing PSA every month, shall I?
Okay, in case you’ve ever wondered, there is a reason nobody usually writes about their characters going potty, and it’s not just because scat porn isn’t everybody’s thing: People haring off to go to the bathroom all the time is boring and interrupts the story. So does bathing unless sex or murder is involved. As a matter of fact, if you think about all of the endless minutiae that make up your average daily life, it’s all boring. Tedious, even. So, unless we’re using it to advance the plot, set a scene, or initiate sexy times, none of that stuff is going to get included in most stories. And that goes double if not triple for movies, where every second of screen time is costing somebody money.
Now, some authors do include hygiene-related things in their stories that they feel are important – L. Frank Baum always had Dorothy wash her face and hands, for example. Other authors may have their characters regularly brush their teeth, wash their hands, change their socks or put on condoms. Do it well and it builds the character as a ‘real’ person, do it poorly and people start to wonder why you’re preaching the gospel of personal hygiene at them. 
Do it in a Star Wars movie and people will probably start asking uncomfortable questions about fetishes and whether or not the movie is rated correctly. Because some things just get creepy when you film them.
In a nutshell, my point is this: It’s okay to wonder when, where and how the characters in a story take care of their daily business. That means you, the reader/watcher, are engaged in the story and the characters, and that’s what we as story creators want – we want you to see the world we created as a real world populated by real people. For the most part, though, we’re just going to leave most of the mundane little details of daily life to your imagination, okay? Because in all honesty, you probably wouldn’t enjoy the story very much if we tried to put them all in.