Cleansing of Saidin I have put a lot of thought into this topic and after reading and re-reading how Rand and Nyneave accomplished this feat. I am a registered nurse and have worked in hemodialysis which the process removes solute (substances) in the blood, water and other solutes in two ways that can be akin to the cleansing of Saidan. First, osmosis a passive phenomenon works is with the movement of water through semi-permeable membrane from a place with lower water content to a place of higher amount in the dialysate bath contains 2 grams of dextrose. Solutes also move by this method solutes move from a place of higher concentration to lower. Filtration is the main key to solute movement from a medium of higher concentration to a lower concentration also as pressure is applied to the fibers of a dialyzer forcing movement of water via pressure along with these solutes are dragged along with water removal. Think of a tea bag you want to get the rest of the tea out you either squeeze the bags with your fingers or while sitting of a spoon you wrap the string around the bag and spoon and pull thus adding pressure. Both processes are done through a semi-permeable membrane. Each dialyzer contains millions of hollow fibers with different pore sizes. The types of solutes are removed from the blood due to the small pore size thus not allowing blood components such as red blood cells from dialyzing out of the body through the dialyzer. Ok, getting back to how Rand accomplished the cleansing based on history we all know that the greatest feats among Aes Sedai occurred with both men and women occurred while they were linked in a circle. Rand’s action with the help of Saidar indeed exhibited how such feats resulted. Using the One Power, Rand’s formation of the tube of saidar acting as a conduit in confining and squeezing saidin while saidin pushed against saidar moving it by pressure through the flower he visualized forming of saidar acted as a semi-permeable membrane in which from Saidin the taint had to pass through the conduit of saidar. Based on the information in Winter's Heart the conduit began from where Rand and Nyneave where and the Saidar and Saidin where forces through the flower of Saidar was situated into the city of Shadar Logoth which did not have the Dark One’s taint but another kind of evil regardless, the taint was dialyzed into that city. Saidin and saidar unable to mix this we know however, saidar’s own immense power contained saidin within this conduit, and once Rand eventually felt the movement of the taint by continuing force of pushing saidin while reinforcing the tube of saidair which exerted against Saidin I believe that just as the male and female Aes Sedai made the eye of the world they may have used this same method however they lacked the protection of a terangreal like the access keys to the Choden Kal’s to buffer themselves resulting in their deaths upon creating to the taint free pure saidin at the Eye of the World. Further, since the evil of Dark One’s taint and the evil of the city of Shadar Logoth could not mix but repelled each other lead to the destruction of the city the example we have evidence in the response of Rand’s wounds in the way they react to each other and their action during the cleansing. One more thing the idea of using up saidin/saidar is not possible because the source was noted in Winter’s Heart coming from everywhere in creation even Shadar Logoth. So despite both evils being different and in a sense two different types of hateful evils obviously the build-up of these evils where responsible for destruction of that evil city when the taint was removed. This is proven in the last book a Memory of Light. This is how I conceptualized this process. For me this is the easiest way to understand and illustrate the cleansing of Saidan.