Is dryness sufficient to purify things like walls and doors from madhi (pre-ejaculatory fluid)? Does painting purify them? And must one who suffers from constant leakage of madhi take precautions against it, or does what it touches not become impure?

The aforementioned items, such as crowns and doors, if they become ritually impure (najis), are purified by water. Fixed walls, being attached to the ground, are purified by drying, according to the Hanafis, once the trace of the impurity is gone. Paint might prevent direct contact with the impurity; it is a strong barrier that covers the impure spot, and the prayer of one who touches that painted wall is not invalidated. A person afflicted with chronic seminal discharge (sals al-madhy) must take precautions and guard himself as much as possible. What comes out after that will not harm him, because impurities that are difficult to guard against are excused.