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 women of the Sahaabah did not wash these pads; the Prophet (peace and blessings of Allaah be upon him) knew about that and it is not narrated that he told them off for that. Al-Tirmidhi (61) and other authors of Sunan narrated that Abu Sa’eed al-Khudri said: “It was said, ‘O Messenger of Allaah, should I do wudoo’ from the well of Budaa’ah?’ – which was a well into which were thrown menstrual rags, the flesh of dogs and other putrid things. The Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘Water is pure and nothing makes it naajis (impure).” This is a saheeh hadeeth which was classed as such by Ahmad, Yahya ibn Ma’een, Ibn Khuzaymah, Ibn Taymiyah and others (may Allaah have mercy on them). 

What is referred to here by “menstrual rags” is the rags which were used for menstrual blood, as al-Mubaarakfoori said in his commentary on this hadeeth. So it seems that they used to throw them away when they were contaminated with blood, otherwise the Sahaabah would not have raised the issue of whether the water into which these rags were thrown was taahir (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 Allaah a great deal (dhikr), reciting Qur’aan and adhering steadfastly to the commands of sharee’ah, and keeping away from myths and stories that have no proof. And Allaah knows best.