Angelina I also think it's legal, but do you really want to expose yourself to security like that?
Well, if the alternative to sit in the plane with a wet diaper or even worse when you have to use Nr. 2, I think that annoyance of the security check is actually the lesser evil. Besides: There is hardly anything people working in these places have not yet seen.
You cannot fly Finland to Australia without a stop-over, simply because no commercial plane can cover the distance.
Typical routes from Europe to Australia have at least one stop-over either in an Arab country (i. e. Dubai if you fly Emirates) or in Asia (e. g. Singapore).