A question about a recipe: Rosti with Gravlax, Caper Berries and Horsradish Cream

I have a question about step 1 on the recipe "Rosti with Gravlax, Caper Berries and Horsradish Cream" from thirschfeld. It says:

"Place a clean towel under a mandoline and grate the potatoes using the julienned blade and let them fall right onto the towel. Bunch up the corner of the towel and rinse the potatoes under cold running water. Twist the towel forming a tight ball and keep twisting until all the moisture is removed."