First of all this glitch is in Der Riese. To do it you need to go to the maindrain near the quick revive machine.

Secondly have a person jump through that hole, then have the person stay there and jump on top of the person,

Then have someone guard that barrier and you're safe.

You cannot move when you're at the top or bottom (you can look around just don't jump).

The glitch is supposed to make zombies not get to you.