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, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
If the water used in washing the impure clothes runs down from them unchanged by the impurity and the impurity was removed from the clothes, then they are pure. There is no doubt that pouring water over an invisible impurity five times is quite enough to purify it. The washing powder residue on them does not harm and does not affect the ruling that the impurity has been removed.
It seems that your question is triggered by Waswaas (obsessive whisperings). Hence, we warn you against Waswaas and getting carried away with it, as that may lead to grave evils.
Allah knows best.