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