Knife hits. By far. Not very easy to pull off though(takes a competent 2nd person). Two people are suggested to do this. One burns & operates the knives, the other inhales.
Get a 2 liter bottle, cut it in half or so, shove the bottom into the top. Mark where you need to cut to just get an inch or overlap or so. Make a second mark where the bottom half of the container is for the ice line. Refine the height of them, and cut off the excess where you marked.
Take a knife, perforate the bottom prodigiously.
Take ice, fill it, you might need to tape it to seal it.
Take two butter knifes and heat them up on a standard oven top, weaving them between the burner coils, on mid-high heat until red hot. Smash a bit of kief or hash between the hot blades, inhale through the ice bong.
Here's an image of the ice bong, pretty simple: