What Gender Is My Hamster?

Well i'm going on vacation in like 1 week and i have a hamster and i cant bring his cage so i have to take him in a hamster traveller Etc. and when we arrive at the hotel my sisters hamster is there too but i dont want my hamster to stay in a traveller that is very tiny... my hamster is named harvey but in the past few days it might be a harvisha (haha totally silly name) my sisters hamster is a boy and well we were olanning on having them in the same cage.. can you explain to me what the boys area looks like and the girls area.. and BTW my hamster only has one hole near his tail and not so ??? whats that mean