>Nice find, please tell me you drank the beer before you cut it open!
Well, I did have help.
Becks makes a 5L keg which is almost exactly the same as the Heineken keg, but uses a different pouring mechanism. The Heine keg is pressurized by a contraption inside the keg (it is tapped like an aerosol can) which can be removed once the top is cut off, while the Becks keg uses carbonation pressure and gravity feed through a tap at the bottom of the keg (shown extended in the photo). The keg weighs 18.9 oz and the 'lid' weighs 0.5 oz. (1.8 oz more than the Heine keg + AGG lid).
The Becks keg is sealed with a rubber stopper with a hole in the middle (gray part in the photo inset), and in that hole is a hard plastic plug (tan part in the photo inset) with a wide cap. When the carbonation pressure runs out you push the plug down into the keg, and then the keg will flow by gravity. After the beer and the stopper are removed, the plug can be liberated from the keg with a bit of finesse. I pushed the plug back into the stopper in the opposite direction (as in the photo) and when it is set back into the hole (with the stopper inverted) it makes a non-sealing 'lid' that rattles when the water begins to boil. The stopper/plug combo can also be used to seal the keg so it can carry liquid.
Obviously, this pot should only be used to boil water or thin soup, since you can't scrub the pot or the tap out. If the pot is full and it comes to a rolling boil, boiling water will shoot out of the hole in the top--beware. The lid can be cut out, of course, to make a snow-melting pot.
So far the tap at the bottom of the keg hasn't melted, although I've been careful to use this only with a canister stove and to keep the flame reasonable. I wouldn't expect it to last long with a stove that caused flames to go up the side of the pot.