Leather clothes are different from normal clothes. Normal clothes made from threads of wool or linen and the like may not be soaked, because this cleans them. However, a leather item may be soaked in water. Only true washing, meaning vigorous scrubbing, is prohibited by the Torah for leather. The reason for this distinction is that unlike cloth garments, which absorb the water that permeates the threads and removes the dirt and stains, leather does not absorb water readily; since water does not permeate it, the water cannot remove the dirt absorbed in the leather. Although soaking leather in water might remove the dirt that is stuck on its surface, the dirt that is absorbed within it will not be removed. The only way to remove absorbed dirt from leather is by washing it – scrubbing it vigorously by rubbing the two sides together or by using a brush or the like. This constitutes the Torah prohibition of Kibus.
Accordingly, if something disgusting fell on a leather item, it may be rinsed off, because rinsing leather removes only what is on the surface. However, one may not rub the dirty spot, because that will remove the absorbed dirt.
It is rabbinically forbidden to wring out a wet leather item. Wringing out cloth garments is forbidden by Torah law because the water is easily wrung out of them; since the wringing removes the dirt together with the water, this is considered a method of cleaning them. But leather garments are not normally wrung out during washing; it is difficult to do, and it is not a particularly good way to clean them. Therefore, wringing them out is only rabbinically prohibited (BHL 302:9, s.v. “asur”).
If leather shoes get dusty, one may remove the dust with one’s hand or a rag, because the dust is not absorbed into them, but merely sits on the surface. However, one may not polish them with a brush or rag in order to shine them (on account of Memaĥek, below 18:6; see AHS 327:4; SSK 15:40).
If clay or mud is stuck on a shoe or piece of clothing, removing it and crumbling it is transgressing a rabbinic prohibition pertaining to Toĥen. But if it is uncertain whether its removal will cause it to crumble to dust, it may be removed. When necessary, even if it is clear that it will crumble to dust, one may remove it with a shinui. For example, mud on a shoe can be removed by rubbing the shoes together, and clay on clothing can be removed by hitting it with the back of one’s hand (above 12:1 and n. 1).