if you want a nice expensive bong, get a roor. they are the shit, although they don't color change. I'd recomend a glass one, they might break but they are soooo much sweeter than a plastic one.

i hope my picture helped.

glass bongs don't have carbs, the bowl, called a slide, sits in the downstem so you pull the slide up to clear the bong. plastic bongs usually have a carb you have to cover.

just made sure you don't fill it up with too much water (bong water is GROSS)

somethings to look for also
~an ice catcher, its a nub so you can put ice in the long part of the bong to cool the smoke, very smooth.

~some downstems have several holes in the water, this helps smooth it also by having more water contact with the smoke

~color changing

if you wanna spend the money you can get a percalator...it has 4-5 water chambers so the smoke gets filtered like a fine vodka but they are like 400bucks

hope this helps!! bongs are sweet!