all depends on size. if it dosen't fit well in a pot then a bleach mix would be a good choice. just make sure to let it dry out for a week or so after rinsing VERY VERY well and make sure there is not bleach smell before you put it in the tank.
Another more natural option would be to soak it in concentrated lemon juice. just apply graciously over the full surface of the DW just like you would the bleach.
Bleach will help to remove tannis some. Not as much as boiling tho.