All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The container that you mentioned is considered to be impure and it is not permissible to use it for ablution, drinking, etc. before purifying it [the container].
The way to purify it is by pouring pure water over the impure place until the water immerses the whole place of impurity. Any place that is touched by the impure water, purifying it should be by pouring pure water over it.
The scholars differed in opinion about the water that is used for removing impurity. Some of them are of the view that it is impure because it has been in contact with an impure place, and acting according to this view is better in order to be on the safe side.
Some other scholars are of the view that this water is pure as long as it is not changed with the impurity, and this view is more lenient to the people.
As regards the pure water that cannot be used to purify with it (i.e., for performing ablution or Ghusl); then it becomes impure by pouring it in a place that is touched with impurity.
Allah knows best.