819. Things That Cannot Be Properly Cleaned

16:10 If something cannot be cleaned adequately - like a sieve, the receptacle of a flour mill, baskets that were used to hold chometz, a grater, a vessel with a narrow neck that cannot be scrubbed inside, or something that has tubes - then immersion in boiling water is ineffective to kasher it.

116:11 If a cupboard is used to store food year-round and sometimes soup spills from the pots, this requires it to be kashered lightly. This is done by pouring boiling water directly from the vessel in which it was boiled. The water is not dumped all at once; it must be poured all over slowly. Tables are kashered with stones heated until they glow. These are placed on the table and boiling water is poured over them. The stones are moved from place to place so that the boiling water can reach every spot. The table must first be scoured; it may be kashered after 24 hours have passed. Nevertheless, many have the practice not to use tables or cupboards even if they have been kashered unless they have been covered.