Any object brought into the TARDIS will be replaced with a block-transfer duplicate if left alone long enough. Since it is now part of the TARDIS this block transfer matter can be manipulated and deleted.
A TARDIS's autocleaning system uses Block-Transfer to remove all unnecessary dust, mud, and debris from its interior. If the operator desires, the systems can be balanced to allow dust and cobwebs to gather in disused rooms. The Autocleaning systems' Laundry Circuits automatically repair, clean, and iron any clothes left overnight in the sleeping quarters.