Ref. No. 2107/44-2128
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
The way to purify impure clothes is to wash the cloth three times with pure water and squeeze the cloth each time until the water stops dripping from the cloth. Even after washing three times in this way, if there is a visible stain of impurity, it is not necessary to remove it, but the cloth is considered pure; and it is correct to pray in it.
"و إن کانت شیئًا لایزول أثرہ إلا بمشقة بأن یحتاج في أزالته إلی شيء آخر سوی الماء کالصابون لایکلف بإزالته ... و یشترط العصر في کل مرة ویبالغ في المرة الثالثة." (الھندیۃ الباب السابع في النجاسة وأحکامها، ج:1، ص:96، ط:مكتبه رشيديه)
And Allah knows best
Darul Ifta
Darul Uloom Waqf Deoband