Wow so much hostility...

Well, Shrooms, let me help you since others think you're ruining your body.

For the downtube, try finding something metal. Go buy a cheapie metal pen, that'd work. The socket's great for the bowl and the window screen is an okay screen, but if I were you I'd hold it over a flame for a 30 seconds or so and see if any fumes come off. If they do, rinse it off and do it again, if you get fumes the second time, you need a different something to use as a screen. Faucet screens are good...balled up metal twist-ties with the paper burned off are good...be creative! lol

I like the O-ring idea for the carb. Very shagadelic, man. The only problem is a mouthpiece. Try taking some wire cutters or tin shears and taking the lip off the can, then maybe your lips can make a seal over the hole that you once drank out of? If that doesn't work, shear the very top off the can and -THIS IS IMPORTANT!- put something rubber over the edge of that. If not, the thin tin could easily cut your face up...not a good thing in a bong.

Hope that helps!