you just described my room mate. i have been using my vaporizer for 2 months, so i didnt touch our bong we bought in that time. i went to use it for old time sake, and the tube smelled like shit, there was black particles in the water, and the water was taking on a brown tinge. the bowl had a mm of resin all over it. it was so fucking disgusting, and thats what he uses to smoke.
i cleaned that shit for him with alcohol and sea salt. i went through 8 q-tips, both sides, to just clean up the bowl. it was like dealing with tar from the street.
some people tote a bong is healthier than a joint cause it fiters with water, but its a moot point when your bong is fucking disgusting. CLEAN THAT SHIT ATLEAST ONCE EVERY TWO MONTHS, AND CHANGE THE WATER OFTEN!!!