Backed up DRAINS..

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My sister lives in a aprtment building with 5 other units. All but 1 of them is rented. There is her and 1 other female living in the building. The main drain backs up every other month, and the landlord told her it was because of Tampons in the drain. Her landlord is threatining her to evict her if the drain keeps backing up. Is it legal to do so? even if she is not responsible? I need some advice and some imput on this situation it will be greatly appreciated. Thanks.