Is it sufficient to dip a garment stained with madhiy into a container of water to remove the madhiy and purify the garment, based on the Maliki school's view that water is not rendered impure unless one of its characteristics changes, knowing that the water was not rendered impure by the introduction of the madhiy into it?

What you did, placing the garment soiled with madhy in a vessel, is considered immersion (ghams). This is sufficient for purifying the garment according to the Malikis, provided the water does not change, and this water remains pure as long as it has not changed. As for the majority of scholars, the water becomes impure, and the garment is not purified if the water is less than two qullas.