In one embodiment, a cartridge includes: a housing having a chamber therein for holding a fluid; a vent at a first part of the chamber; a porous fluid holding material in the chamber; an outlet from the chamber; and a hole extending through the fluid holding material from the first part of the chamber to a second part of the chamber at a location away from the outlet such that the second part of the chamber is vented through the hole but the outlet is not vented through the hole.