But Onan knew that the offspring wouldn't be his own heir, so whenever he had sexual relations with his brother's wife, he would spill his semen on the ground to avoid fathering offspring for his brother.

Every garment (including leather) on which the semen is found is to be washed with water, and it will remain unclean until evening.

When a man has sexual relations with a woman and the man releases semen, both are to bathe with water, and they will remain unclean until evening."

These are the regulations for one whose discharge of semen causes him to become unclean because of it,