I would use distilled water as my first choice for thinning high VG, maybe starting at 3-5%. Vodka will work too, but you need far less for thinning, maybe 1%. If you use vodka, it's good to let the bottle sit open for an hour or so, letting most of the alcohol evaporate. Either way, add just a little at a time until you get the flow and wicking you need. Good luck!