You should also read up on how dirty that tank is likely to be & get into the practice of distilling your solvent before attempting to make medicine.
http://future4200.com/search?q=mystery+oil
- How to distill solvents
- Distillation before extraction?
- Mystery oil with no opinion just facts
- Cleaning up Butane/Propane
edit: yes, if you insist, you can get the genie back into that bottle via the hole it came out of. can you tell us what temp you would need to hold that tank to achieve zero back pressure?