Can there be active THC be trapped in the evaporator?
When burning a blunt, joint, doobie or whatever, THC evaporates (bp of tetrahydrocannabinoles is around 155 °C). Depending on 


the length of the "object" , related to the temperature gradient between the front and the mouth piece, and
the type of the "filling" and its adsorptive properties


a part of the vaporized material might condense and/or get absorbed in a colder region of the filling. Similar effects, such as the enrichment of nicotine in the stump of cigarettes have examined.

It is however unlikely that any of the transported and reabsorbed components can be inhaled from a cold "reactor". The relevant components are no longer in the vapour phase and the vapour pressure of the tetrahydrocannabinoles will be too small.