Interesting question.
Can't help because we don't have an answer to this one on record, and I don't use 0 nic. However you can measure it yourself quite easily if you have the two different liquids, and then adjust the more viscous one so that it feeds better.
It's done like this: paint sprayers need to adjust the viscosity of their materials because this is critical to their work, and they also need a simple test that 'works in the field'. A fancy lab test is no use to them, they have to add thinners to paint on the fly to stay in business. They use a thing called a viscosity cup, which comes in different versions but is commonly a simple funnel calibrated with quantity levels and with a small exit hole. They pour in some paint and time how long it takes to drip out, then add thinners to make it flow faster, to a set point (quantity vs time). The viscosity cup is calibrated to work well for their purposes.
The main difference between their needs and ours is that they work with very large quantities - litres - but we work with a thousand times less (exactly in fact) - ml or millilitres. Therefore the tools need a bit of a kludge to fix them for our use.
Howto
Take the smallest kitchen funnel you can find. You can buy them in sets in a dollar store / pound shop, and you can use the tiniest one in the set for this.
Get a syringe marked in ml, a watch or clock that you can read seconds off easily, a bowl, and a marker pen / felt pen / laundry marker that writes successfully on the plastic of the funnel - test it on the outside.
With the syringe (or a pipette), draw up and roughly measure a suitable amount of water for trial purposes - say 3 ml.
Place your finger over the hole in the bottom of the funnel and put the water into the funnel.
Let your finger off slightly so the water drips out. See how many seconds it roughly takes, looking at your watch / clock placed on the table beside you.
This is the outline procedure for the viscosity test: a set amount of liquid drips out of the funnel in a set time.
Now dry the funnel off and tape up the spout with sellotape, duct tape or whatever.
Puncture a very small hole though the tape and run the water drip test again.
Get the hole size about right.
Mark a level on the inside of the funnel, to save time, if you want - maybe for 3 ml, 10 ml, or whatever.
Now run the test with the actual materials you need to test.
Add thinners (DW, alcohol, PG or whatever) to the glycerol to make it less viscous, as needed.
Terms
viscous = thick, gloopy
more viscous = thicker, drips slower, feeds slower, wicks slower
less viscous = thinner, drips faster, feeds faster, wicks faster/easier
