If you get 5lt of Propan-2-ol (99.9%) and 2 bottles (2x118ml) of pure lanolin (typical quantities available online) and mix them all together you'll get a 21:1 mix and a lifetime's supply, almost.

Listening to the experts on the net, anywhere from 10:1 to 25:1 seems to work. But 21:1 I know works and this way you have no leftovers and it makes measuring a doddle. Just let the alcohol evaporate before you size.