Chromic: If you have any choice, go for the glue that is used to cement narrow-fitting hard-PVC pipes together. It will be highest in THF and lowest in polymers. Over here that is a clear, tannish, very viscous liquid. The gray stuff (again: over here) is used for wide fittings and has a lot more fillers in it.
isop: Sure, the liquid obtained by the separation is by no means pure THF. But the idea is that you distill it. Collect very little below 66°, a large fraction between 66° and 75°, have some polymeric crap fall out of solution at this point (so yes: you were right about that). Left in the flask is said crap and water, that only faintly smells of solvent. I know this is not scientific proof, but what would your guess be?
Hansje high in proteine and fibre!