Problem:
What is the probability of conception in situations when sperm isn't directly ejaculated into the woman's vagina, like:
The man's or the woman's hands come into contact with sperm, for example when removing a condom. (Perhaps after washing them,) the hands later touch vagina, for example during foreplay to another intercourse.
The man and the woman taking a bath together, the man ejaculates into the water.
The man ejaculates on the woman's body, perhaps on or around vagina but not inside. (In this case it could also make a difference whether the woman has shaved pubic hair or not.)
The man ejaculates during receiving oral sex, (perhaps the woman rinses her mouth), the couple kisses, the man performs oral sex to the woman.
In all these situations, it seems possible that a tiny amount of sperm is eventually transferred into vagina indirectly. And since just a single cell is enough to fertilize, it seems that there is non-zero probability of conceiving.
Required:
Question 1: How much care need to be taken to prevent conception in such situations?
Question 2: Does simply washing sperm away with water (+ soap perhaps) eliminate it?
Explain the answer step by step.