The basic principle for purifying clothes from any impurity (najasa) is to remove the impurity itself. If the impurity has a physical substance, such as feces or blood, it should be physically removed first by scraping or wiping it off.

After removing the substance, the affected area must be washed with water until the traces of the impurity are gone. The traces are its color, taste, and smell. One may use soap or modern detergents to aid in the removal, as the goal is purification, and these substances help achieve that effectively.

The amount of water or the number of times it must be washed is not specified in the Sharee'ah. The requirement is simply that the area becomes clean and the impurity is removed. Once the traces are no longer apparent, the garment is considered pure.

This is based on the hadith of Asma bint Abi Bakr, who asked the Prophet (peace and blessings of Allah be upon him) about menstrual blood on clothing. He instructed her to scrape it, rub it with water, and then wash it. This shows that the objective is the removal of the substance.

If a stain or smell remains that is very difficult to remove after one has made a reasonable effort to wash it, the garment is still considered pure, and this is overlooked due to the difficulty. The religion of Islam is one of ease, and one is not burdened with more than they can bear. Therefore, once a diligent effort has been made to clean the impurity with water, any faint, lingering traces that are hard to remove are excused.