1- Semen is recognizable, as it is thick and sticky. Hence, if it is not like that, then probably it is not semen, so, you do not need to perform ghusl. However, if you are in doubt, and you want to perform ghusl, then you need to perform ablution as well. The intention in both cases is ghusl Janaba. The difference is that in the first case, you don’t need to perform ablution with ghusl, while you have to perform it in the second case.
2- If the washing machine washes two times with pure water, with spinning in between, then it is OK.