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.
If you are certain that water has been poured over these impure clothes in a way that the water covered the entire impure spot (if the impurity was not visible) or to the extent that the water totally removed the impurity if it was visible, then this is enough to rule that the clothes have become pure.
However, if you yourself wash the impure spot from the clothes before sending them to other people to wash them so that you make sure that the impurity is removed and avoid doubts, then that would be good.
For more benefit, please refer to fatwa 229372.
Allaah knows best.