Portal 2: How do you create bottomless pits?

Does anyone know how to create a bottomless pit in your map? I know there is a tutorial on this, but the tutorial does not say how to create the pit. (Just about a trigger_hurt) Possibly the sky texture? And maybe props? Unless there is a better way.

I used a pitch black texture for my floor in the pit. But it doesn't really matter if you have fog (env_fog_controller) in your map. Also, I made a trigger_once for when a player fell down, and it'd activate an env_fade (it makes the screen fade to black) and an entity that reloads the latest save game (not sure what it's called).

Before the player was even able to see the floor the game was already reloading a saved game, so it created the illusion that the pit was even deeper than it really is.

What did you use for the pit in your map Mortal Dream? Because in that map it looked like there was no floor.

I'm pretty sure it was "tools/toolsblack"

Thanks, I'll try that.