Actual semen has been found up to a week (7 days) after intercourse in some women. Keep in mind a few things; the vagina secretes a natural discharge which helps flush (clean out) semen, and gravity eventually will play a role in the semen leaking out on it's own. Yes, some can be washed away, but there would still be some present in the vagina. Urinating could flush away some of the semen around the vulva, but there are no guarantees with that either. I hope this helped some.
Sperm can live and be active, inside the vagina, from up to 3 to 5 days. Pregnancy is possible ( especially if protection/birth control wasn't used) within this time frame, when sperm is present and alive within the vagina.