Is your drain sluggish or backed up? It's a good idea to clean your drainage pipes to keep them free of odors and clogs. Here are a few simple steps to keep your drains odor free and draining properly.
1. Every few days run very hot tap water through the drain. This is one way to keep a drain free of odors. Treat any partially clogged drains promptly.

2. Put a tablespoon of baking soda into the kitchen drain about once a week, then slowly pour in 1/4 cup of vinegar or lemon juice and let it stand for 30 minutes. Next run hot water through the drain to eliminate minor buildups and odors.

3. Pouring a strong salt water (brine) solution down the kitchen sink drain will eliminate odors and keep grease from building up.

4. Consider buying a drain cleaner solution if you have drains you can't clear out naturally. Be sure to read the label regarding the product suitability safety for your drain pipes. (Some chemical drain cleaners will harm plastic drain pipes). Make sure the solution is safe for plastic pipes or a garbage disposal. Be sure to follow the drain cleaner instructions.

5. Alternatively, consider a natural drain cleaner even for blockages. Remove any standing water then pour 1/2 c. baking soda into your drain. Follow this with 1/2 c. white vinegar. The baking soda is basic and the vinegar is acidic, so they will react with a churning action should break up the blockage without using any chemicals.

6. Call a licensed plumber for anything beyond regular drain cleaning and simple unclogging of drains.

From: http://www.ehow.com/how_17961_clean-sink-drain.html