i've hit many a gravity bong pisser and waterfall in my time. but i must say that the water filtered grav is the absolute best. used the downstem from my 3bubble amber hooka (pics here)
http://forum.grasscity.com/showthrea...770#post846770
heres 2 pics of the bad boy in action!
http://img462.imageshack.us/img462/8...gravhit8te.jpg http://img462.imageshack.us/img462/3425/dsc002391oa.jpg
most popular devices are 2 litre bottles and arizona iced tea gallon jugs.