what i usually do is run it under hot water, which will get rid of a lot of gunk, then let it sit overnight in cup or bag of rubbing alcohol, then do the hot water again, then use some more rubbing alcohol + salt (the salt works as an abrasive) and swish it around the pipe (make sure to cover the mouthpiece/bowl/carb). this will get rid of just about everything in there. don't bother buying any cleaning products for bowls, they're mostly just rubbing alcohol and salt