If a dish or cloth had pork impurity on it, but was washed but a stain/colour of it still remained, is it pure? how about everything that was washed with it? If there is a dish that cannot get clean and is from previous tenants, and may seem a bit sticky and just cannot get clean but is not just a stain, but we don't know what it is, is it impure? as it is a baking tray part of the oven and we cannot throw it away. I put greasing paper on top but I worry its not enough as the whole thing is sticky and does get touched with food quite a bit.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

When in doubt about the purity of an object, then the default state is that it is pure. The basic principle with regard to this matter is that all things are pure unless there is evidence that they are impure; mere doubts are not enough to assert the object impure.

If it is known with certainty that an object has become impure, then it should be washed under running water until the impurity is removed. Any of the color or smell of the impurity that is not possible to remove is pardonable.

The impurity of a the flesh of swine should be purified by washing it seven times, one of which should be with dust or soil.

However, you should totally disregard such Waswasah (obsessive whisperings) and ward them off because indulging in such Waswasah leads to grave evils.

Allaah Knows best.