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