Related for Zevachim 158:12

The earthenware bed-chamber (following Lieberman, חרסן not התמד ["inferior wine created from husks and stalks of grapes"]) of a zav or of a zavah [who experienced his or her] first or second [emission] is impure; [but as to] the third, it is pure. In what case does this apply? When he (or she) [did not] put water inside of it (see Yerushalmi Ter. XI.4.11), but if he (or she) did put water inside of it, even the tenth is impure. Rabbi Eliezer ben Ya'akov says, a third [is impure] even though he did not put pure water inside of it.