when you smoke  hemp it leaves a residue 
 tar   inside   the  machine,  which   is 
 extractable  with the help  of  a  metal 
 rod. be wary however, that the hemp  tar 
 is  not as viscous  as  you may think... 
 it'll quickly get  on  your fingers  and 
 boobs... and it's  hard to get off. very 
    sticky business indeed. most people   
 just   get   rid   of   their   machines