The gravity bong you made in college out of an empty 2 liter bottle was a great prototype, but it's about time you graduated (from plastic, anyway).
The new line of glass Gravity Bongs from Pulsar has a similar setup to the traditional model of a gravity bong : a base container for water and an inner dome fitted with a bowl.
Once you light the herb, slowly lift the inner dome. The water creates a vacuum, gently pulling smoke into the inner chamber. When you're ready for a hit, simply remove the bowl, place your mouth on the joint, and let the inner dome slowly slide back into the water while inhaling. This model is popular because it saves your lungs effort on the initial pull and creates reliably rich smoke every time.
So maybe we didn't re-invent the wheel, but these Gravity Bongs have all the upgrades their ancestors were lacking. Made from quality borosilicate glass, the base of the interior dome is lined with a black silicone guard to prevent glass-on-glass damage. Each bong is topped with a female joint connection and includes a compatible male herb slide. Just add water and this setup is complete!