I made a bong that doesn't leak, is reasonably durable, small and portable. I got two slightly different sized pen tubes, melted the smaller one so it would form a 90 degree angle then stuck one end in the larger pen tube and used electrical tape to seal it. I then took the mouthpiece off an old pipe and stuck the pen-stem in it and taped that up. Then I just cut a hole for the stem and shotgun and taped it all up. Suck out the bottle top and enjoy.

My most aesthetically pleasing pipe was a hollow M&M's figurine. I just stuck a pen tube in his ass, taped it and then gave him a tinfoil hat/bowl. Not the best functionally speaking, but I enjoyed it.