We're able to filter about 6G of 100 proof using 5.5lb of carbon. Up until the 5th or 6th gallon, the product is tasting very neutral and towards the end, the flavor from our grain bill starts to pull thru.
Make sure you rinse your carbon first, fill up a bucket with desired amount, use hot water to rinse, stir, and allow to sit for a bit. Most of the carbon will settle at the bottom, pour off the liquid from the top of the carbon, refill ( a couple inches above where the solids sit ), stir, and add carbon/water to whatever vessel you are using as the filter system. We have a 6 foot, 3" diamater column with a hopper on top, coffee filters on the bottom held by a giant hose clamp. Once the water from the top of the hopper has dropped, start adding your alcohol. I use hot water as you can tell by feel when the water is starting to turn in to alcohol. Of course, I go by taste too. The first jar will be a little diluted but everything after should start drippingg out good and neutral. It is a time consuming process but it works depending on how much you need to filter. I've noticed that the higher the proof, the more flavor pulls thru, so I definitely proof down to 100 or less.
Any other tips I can think of besides carbon filtering-
make sure your cuts are on point
add more hieght, packing, or plates to your still