Is It Mandatory in Islam to Wash Used Sanitary Pads Before Throwing Them?
Question

It is the practice of my fellow Muslim women friends to wash their feminine pads used during menses before they would throw them away. Is it true that it is obligatory to do so even though we are using disposable feminine pads which we are not going to use again? A lot of cases of hysteria and other disturbances are being said to be caused by not washing the pads properly before throwing them away by those afflicted. They say that the devil of the jinn likes to eat menses blood left on unwashed pads and would then harm the one who didn’t wash it.
Praise be to Allah.None of the trustworthy scholars have stated that a woman has to wash her feminine rags or pads which may have traces of menstrual blood, if she is going to throw them away and not use them again. Rather it seems that the female Companions did not wash these pads; the Prophet (peace and blessings of Allah be upon him) knew about that and it is not narrated that he told them off for that. 
At-Tirmidhi (61) and other authors of Sunan narrated that Abu Sa`id Al-Khudri (may Allah be pleased with him) said: “It was said, ‘O Messenger of Allah, should I do Wudu’ from the well of Buda`ah?’ – which was a well into which were thrown menstrual rags, the flesh of dogs and other putrid things. The Messenger of Allah (peace and blessings of Allah be upon him) said: ‘Water is pure and nothing makes it impure.” This is an authentic Hadith which was classed as such by Ahmad, Yahya ibn Ma`in, Ibn Khuzaymah, Ibn Taymiyah and others (may Allah have mercy on them). 
What is referred to here by “menstrual rags” is the rags which were used for menstrual blood, as Al-Mubarakfuri (may Allah have mercy on him) said in his commentary on this Hadith. So it seems that they used to throw them away when they were contaminated with blood, otherwise the Companions would not have raised the issue of whether the water into which these rags were thrown was pure or not. 
There is no sound basis for what your friends have said; rather it is a myth which has no basis. Such notions are widespread among the common folk, so you have to ask for proof and evidence, and refer to the scholars and books of knowledge. You have to reject these myths and warn people against them. Each person must protect himself against the evils of the devils among mankind and the jinn by remembering Allah a great deal (Dhikr), reciting Quran and adhering steadfastly to the commands of Shari`ah, and keeping away from myths and stories that have no proof.
For more details, please refer to the following  answers: 7776 , 13948 , 1326 , and 44980 .
And Allah knows best.