Apparantly it used to be a habit among some tribes of Australian Aborigines that, when they spotted a stranger travelling on their land, they would sneak along behind him and spy on him for about two days, to make sure he wasn't a demon. The way they knew he wasn't a demon was if he occasionally passed water and ate and the like.
Loquax said:
Are you telling me that it's okay for a character not to eat or sleep if the process is boring?
Yes. But what you seem to be missing is that if the person is doing something else for 24 hours straight and hasn't done anything, that fact
becomes interesting.
Realistic but otherwise boring details should be mentioned exactly often enough that the reader's immersion in the story is not broken by the absence, and no more often than that. This number can be zero times if that's what it takes and it can be assumed to be covered elsewise, but it can also be fairly often, if, no really, the lack of sleep or bathroom breaks would be telling.
What qualifies as a boring but realistic detail *also* varies. We've covered examples above of interesting or inconvenient bathroom breaks.
The mention of washing, for instance, can be as little as, "He showered, and rushed out to the site.", or a whole scene in itself, if you're talking about Psycho.
Meals are often a good way of revealing character, or theme, or places where exposition, revelation, and plot can be put in, but sometimes they're just a bit of fried chicken, and can be left out in the chapter break.
Driving from point A to point B is a yawner - unless you're writing a road trip, or there's a snowstorm, or...