Combine the yeast and 1/2 cup warm water in a small bowl. Let rest 5 minutes.
Combine the potatoes, potato water, butter, sugar, salt and tap water in a very large bowl.
Mix well, then add eggs, yeast, and 2 cups of the flour to the potato mixture. Blend well with a wooden spoon.
Add flour, 1 cup at a time until a soft dough forms and all 8 1/2 cups are incorporated.
Once everything is mixed, spray with non stick spray or pat with oil and cover with plastic wrap until doubled in size--2 hours or so.
Once doubled, divide dough in half and gently knead on a floured surface sprinkling with flour as you go just to keep it from sticking, about 5 to 7 minutes until the dough is smoother and more elastic. Roll one into a 12x18 inch rectangle.
Mix the sugars, cinnamon, and vanilla in a bowl.
Spread half the butter on the dough and sprinkle on half the sugar mixture, reserving the rest for the other half of your dough.
Roll from the long side and cut slices about 2 inches thick or use dental floss or string to cut slices.
Place in a greased 9x13 pan.
Repeat with other half of dough. (You can freeze rolls at this point if you want to).
Cover with greased plastic wrap and rise in a warm place 30-45 minutes until doubled. You can also place the rolls in the refrigerator overnight and bake them in the morning (they will not need any more rising if you have them in the fridge overnight).
Bake in 350 degree oven 30 to 35 minutes. Tent with foil halfway through if they get too dark.
Cool 15 minutes and the drizzle with icing.