Gabe's Car Wash.

[retrolinkx]

In Left 4 Dead, The third level of No Mercy, has a car wash, that is apparently made by Gabe, called "Gabe's Car Wash"

It can be found just before the Gas Station, behind the destroyed oil rig on the wall. (I found this with Noclip)

It is, I believe supposed to be the building on the left of the picture, in which there is a car, and usually some Molotovs and pipe bombs on some shelves in the corner.

I couldn't really get a better picture than this, but I could try if it's DYKG material.

[BeamuFireu]

Just use imageshack or imgur instead of postimage.

[retrolinkx]

First thing to come up on Google, my good man.