Here is my 100% Achievement Guide!
So soon after getting past the conference room, you see three guys all sitting in a cubicle toilet, they need toilet paper, but where is it?
Look in the toilet to the left of those guys and interact with it to get a screwdriver. Note the markings on the walls.. They are directions that you need to navigate the pipes we are going to be going through.
Once screwdriver is in hand, go left, open up the grate and climb through.
The directions are Right, Up, Right, Up, Left, Up, Right, Right, Down, Left, Left, Left and you find the toilet paper.
You have to go back now, and there is only one way... The way you came, so use the directions above but opposite.
Or of course, if you would rather see how i have done it, go to 13:30 in the video.
Hope this helps!