Dry the stain 3 xs a day. I do every time I noticed it wet! Walaa gone barely noticeable. I just 5 days will sent pic in 3 weeks!! The wetness allows dirt to stick and bacterias to grow. Works.
It doesn't have to be a raw diet. In fact too much red meat can also be a cause of tear staining.Have you considered a change of diet ?
It is reported that changing to a raw diet can stop the tear staining !