Basically exactly what the title suggests. How to make? Very simple. Get the bottle (preferrably empty, dumbass), get a nail and a hammer, or two things similar that can punch a hole in the glass. A metal bowl to attach to the lid is always nice, but not required. You can see the bowl on the lid of this particular bottle. Now, the secret (not really): Every sobe bottle has a weak point in the glass at the base of the bottle, you can see where the glass gets thinner at one point. Simply place the nail on that point, and exert force. How to use? Fill it with water (keeping your thumb on the hole you just created), screw on the cap, put shit in the bowl, hold the lighter on it while letting the water pour out of the hole and thus creating a suction that will draw the smoke into the bottle. When the water's gone, unscrew the cap, and breathe in heavily. The hole works as a carb. That's basically all. Have fun.
Here It Is
A straight up view of the gravity bong.
Here's The Hole
A shot of the hole. The weak point is on the back of the bottle at the bottom. It shouldn't be hard to find, it's the only thing that looks different on the bottle. Don't ask why it's there, the reason is quite obvious...the people who make Sobe are clearly pot heads.
Here's The Bowl
A shot of the metal bowl on the lid. You can punch a hole in the metal and insert the bowl, or you can just make a large indentation in the lid and poke smaller holes in it to create a make-shift bowl.