Separate liquid and potato starch from grated potatoes by pouring the mash into a linen sack or cloth and then squeezing to remove all the liquid. Squeeze liquid into a separate bowl (don't throw away). Potatoes should be dry. Set potatoes aside in a separate bowl.
Once water and starch have separated (#5 above), pour off water (and save) so that only the starch remains.
Potatoes: the recipe needs high-starch potatoes, in Canada, Russet potatoes will do.
To prevent rusting (potatoes turning colour, becoming grey): after potatoes have been peeled, place sliced potatoes into cold water with some vinegar or lemon juice; work quickly to reduce time between when the potatoes are mashed to when they are formed into dumplings and boiled.