Probably preaching to the converted here I know, but when using butane, it pays to be careful what type you are using, the same goes for propane; often they will both contain a light oil fraction to keep seals of the storage container they are in from perishing. A 9kg propane BBQ gas bottle can contain as much as 20-30 ml of light mineral oil, once this in in the extract mix it’s PITA to get out and it will end up in the extract, smelling vaguely strange and giving everyone a headache. Not ideal obviously.
The ultra purified butane is the stuff to get. I have used the venti butane mostly because it evaporates cleanly but most purified should be ok. If in doubt, do a evaporation test on a peice of clean glass, if there is any residue, don’t use it.