Very detailed rules are laid out for quarantining lepers, menstruating women, men who experienced nocturnal emissions, etc. Start with Leviticus 13, it's not hard reading (depending on how archaic the translation is).

Not exactly about a number of days, but Deuteronomy 23:12 instructs those going to battle to carry a shovel so they could bury their excrement and not leave it exposed in the camp, lest God abandon the camp and not defend them from their enemies. (After all, God is holy and poop is not).

I highly recommend reading the original literature and not a secondary source. The way the text weaves reasonable ideas with superstition, threats of abandonment and punishment with messages of hope is a fascinating window into the way people thought in another time and place.

I recall a lot of mentions of cleansing rituals. Including a way to make an antibacterial soap. Been awhile, so I may have some details wrong.

Becoming sick was near equivalent to being a sinner, so good hygiene and righteousness had some overlap.

Follow these rules, you won’t get sick. Got sick? You didn’t follow the rules.

Harsh reality, but a harsh time.

Off the top of my head, Numbers 19 applies for caring for the dead: https://biblehub.com/niv/numbers/19.htm

Menstruation is in Leviticus 15: https://biblehub.com/niv/leviticus/15.htm

... in fact, most of Leviticus is about "clean" vs. "unclean".

the book of Leviticus? Its the 3rd book of the Torah/Old Testament of the Bible. A lot of it is there and would be where I would start.