I loose about 6%. Using 1.7 liters carbon cleans up 4 gallons really well; and 5.5 gallons fairly well. Most sources advise one to dilute the product down to 40% - 60% ABV before filtering. I don't dilute, but instead run it through at 90%+. Let the carbon absorb water for at least 12 hours (it expands). Fill the filter with wet carbon keeping it wet the whole time.
After pouring the alcohol in the top of the filter, one can tell exactly where the alcohol is in the filter; because the alcohol creates heat where it meets the water. This way you can tell when the water is almost clear of the filter and when you should begin to collect the spirit. As the last of the alcohol absorbs at the top of the filter, add water (4 cups in my case) to push out the remaining alcohol. When this 4 cups is gone stop the filter: this is your spirit. Finish by collecting anything that will drip out and add to later runs through the still.
Rinse the carbon in hot water, then boil and drain. Dry carbon. Bake at 550 derees F for at least 4 hours or until bad smell goes away. Good ventilation is necessary as the fumes are toxic. Carbon can be reused hundreds of times.