What is the ruling on purity (tahara) and prayer for one who suffers from a pilonidal sinus that continuously or semi-continuously discharges blood and pus? And is it obligatory to wash it before every prayer, given the hardship involved?

The emission of blood and pus from a fistula located outside the anus does not invalidate ablution (wudu), even if it is abundant. The blood that issues from other than the two private parts (i.e., not from the penis/vagina or anus) is considered impure (najis) by the majority of scholars, and the body and clothes must be purified from it before prayer. However, if purification is difficult, one may pray in this state while using a patch to prevent its spread.