You could have one male w/ a group of females. This might be good if you don't want a lone male to be by himself. If you want to keep the genders separate, then that's fine too. Its just a matter of preference. I've done both ways. I personally like keeping the males separate.
A bath before reintroduction may work. And maybe don't keep him away from the 'boy tub' for long as he could lose his place in the hierarchy. I know a few people who breed show rats will only place a male w/ a female between a few hours to overnight, then reintroduce him back w/ the males.
In the end, I think it really just depends on the males if they fight or not.