An explanation to those confused:
It does not use any hidden elements, it is simply a sign on the far left of the screen that (due to poor checking while drawing the sign in the code) causes it to overflow to the right of the screen, What people are assuming is 'Invisible Pipe' is simply obscured by a black box from the sign.
You can easily see the sign on the screenshot on the site

Here's the same save but without the magic sign: