Couldn't you use a distiller to capture the vapor as you SLOWLY heat the mixture and decant the ethylene glycol for reuse?

Gallons are a volumetric measure so you have to know how much a standard volume unit of water weighs to convert any other volume to weight. Fortunately someone thought of that when inventing the metric system and chose water as the volumetric standard on which to base the conversion of milliters (volume) to milligrams (grams). 1 cubic millileter of water is equal to 1 gram

1millitre of H20 weighs 1gram

the conversion factor from the volumetric liter to volumetric gallon is:

3.78541 litres/gal or

3,785.41millitres/gal

So one gallon of water = 3785.41 grams or 3.78541 kilograms

conversion factor of kilos to pounds is 2.2046

2.2046*3.78541= 8.3454 pounds