Don't feel that it is necessary to use a tumble dryer to felt your items. It is not, it is a preference for me as it takes a shorter time to felt my items. I would only use a washing machine for items which had been knitted rather than wet felted. The best thing you can do, is buy yourself a heavy duty bamboo blind, used or new, and roll your slippers inside it. Keep on turning the slippers inside the bamboo blind until they start to shrink from all sides. You will notice that the template starts buckle as the fiber shrinks. After this stage you can easily rinse it in hot and then cold water and then drop it onto a counter surface. You can even shrink items by hitting them against an outside wall in the area you want it to shrink. After this you can shape as desired. Slippers can be shaped using your own feet, on wooden shoe lasts, polystyrene lasts, resin lasts or even use some soft plastic shoes you might have lying around at home.