Dogs and cats also carry diseases, and they are as dirty as, if not dirtier, than rats.
I've had three of them and they clean themselves every half hour. You only have to bathe rats if they get into something, (once my rat got honey on his head, it was hilarious) in which case you'll have to be careful. All of my rats hated water, and my hands would get scratched up because they were so frantic. (Don't worry! It doesn't break the skin.)
I have never been bitten, ever. Every time I woke up in the morning I went straight to the cage and took out the rat I had at the time. He or she would sit on my shoulder, in my sleeves, or against my chest while I got ready for school, and then I'd care for them (change the litter, replace food and water, etc.). When I got home the rat would be jumping up against the cage until I let it out, and they'd be with me until I ate dinner and again until I went to bed- everywhere!
They are escape artists, so be careful. Fortunately they're not hard to catch, once my rat Kenzy escaped and when I woke up the next morning she was asleep in my shirt.
They are very trusting friends, and also nearly indestructible (I slept with one in bed, after all) and it takes a LOT to get them to bite. They're actually not different enough to be classified as a different species from their wild counterpart, the brown or Norway rat, but are 100% domesticated and are like low maintenance dogs.