We have been breeding rats for about 6 months now and i have NEVER had a problem with the smell ever since day one. I keep them on Aspen bedding and I usually keep 4 to a bin, of course separating the maternal mothers and their babies.
Once a week I separate all the rats in two groups. I have about 11 breeders (6 are hairless) and 15 almost big enough to feed off, plus a few hold outs. Well I separate them into two groups (13 per group) one bucket for each group, then I drizzle them with baby bubble bath soap (cherry ). Put a mess lid on it, add some water, swoosh them around, drain the bucket, and then rinse them off. You have to be quick cause they will be trying to poop as much as possible. I then remove the lid let them sit in the bucket for about 20 min, they are so busy grooming themselves, that they don't even try to get out. While they are drying I change out the aspen in their cages and they are ready to go !
Like i said, if you do this once a week (maybe every 2) it eliminates the smell and you can actually have guest in your home without worrying about them thinking your house is a petting zoo!! It takes me about 2 hours to get everything done but it is well worth it!!
Thanks everyone!

P.S. I left out a step or two, if your really dying to know you can just pm me.

-M