Question: Is it permissible for one to discard ones hair & nails down the drain? In some cases e.g. shaving in the shower, this can’t be avoided.
Answer: Unwanted hair and nails should be disposed of by burying it in sand. It is makrooh to flush it in the toilet or throw it down the drain.
And Allah Ta’ala (الله تعالى) knows best.
Source: Mufti Online