Filtered Smoke Grav Bong

I have tried doing this on attempts but cannot quite figure out what needs to be done due to my lack of science.. so far I took a tube about as long as the bottle and had it going from the cap down, but then it only filled the tube with smoke.. does anybody know what needs to be done or hav you accomplished it?

(sorry if typings bad i just took 2 regular gravity bongs of "green crack")

You need to make sure the cap and around the tube is completely air tight. Because if it isnt the air will be drawn in through there instead of down the tube and up through the water.

Build a Blissett Bucket

blog.myspace.com/lutherblissett

just make a normal one but hold a roach in your lips while you hit.