I say, and with God's success: The invisible impurity is purified by washing it three times with wringing each time if possible: such as a garment, on the condition that one exaggerates in wringing during the third time as much as his strength allows, or it is washed and left until the dripping ceases, and then so on. If wringing is not possible, the contaminated item is placed in running water, or a large amount of water is poured over it and the water runs over it for a day or a night, thus it becomes pure without wringing or triple washing; because it is presumed that the impurity has been removed from it, and the estimation of a night is to cut off doubts. Refer to: Al-Wiqayah p. 131, and Fath Bab Al-Ianayah 1: 245, and God knows best.