To describe how good this “pre-wetting” method works is easy. To purify 5 liters of alcohol 40-50% one normally needs 1 tube 40 mm x 1.5 meter, then one more to take the last 10% volatiles that remain (this can be used again next time as first filtration).
With the pre-wetting method, the same can be done in one filtration in a 1-meter tube, sometimes shorter.

In the purification process, three zones are formed in the carbon bed (the pipe). At the top, nearest to where the unpurified alcohol is poured in, is a zone known as the consumed zone.Then comes a zone where the carbon is working and absorption of impurities is constant. This is the Purification Zone (MTZ).
After the MTZ zone, furthest down in the pipe, is a zone with activated carbon, which has not yet caught any impurities: unconsummated carbon.During the purification process, the consumed zone and the purification zone will move farther and farther down the pipe until the unconsummated zone comes to an end. When this happens, all remaining impurities will pass through the bed and the alcohol filtrationceases.

Absorption occurs in the MTZ. The MTZ should be as short as possible. The larger the carbon grains (the smaller the contact surface) and the faster the speed of filtration (HSV), the longer the MTZ is. If the grains are 2-3 mm, the MTZ becomes longer that the
pipe, and purification does not take place.