A few tips to reduce odor:
1) Ventilation is the key. No one (including your ratties) wants to breathe or sit in stagnant air. It makes a huge difference. It also prevents RI.
2) Weekly cleaning at the minimum. (It's the soiled bedding that has a bad small. The rats have very little odor themselves. They are very clean little critters. And yes, males do have a stronger odor. I call it 'buck grease'. lol)
3) Quality diet (poor diet, such as dog food, will make your rats oily. The excess oil production makes them smell terrible)
4) Vanilla extract in their water will help body odor
5) Some baking soda sprinkled under the bedding will help too.
6) Don't overcrowd enclosures.