isopropyl works,people say there is better stuff.
orange chronic,couple other orange ones.
you can run hot water through it a lot.either way your going to need to shake the bong....it won't break don't worry
you can also fill the bong wo some water,add rock salt/coarse salt and keep mixing until it won't dissolve anymore,then keep shaking the Salk chunks will help scrape the res out.