Both the bathroom and the kitchen sinks are an excellent source of spreading odor. With time, the pipes gather a considerable layer of grime that fosters odor. After you thoroughly wash the sink and tub, the smell become pleasant, but within hours the unpleasant smell returns.
A very effective solution for cleaning sinks is baking soda. Pour a cup of baking soda into the drain, then pour vinegar. The resulting foam will thoroughly clean the pipe. This process should be repeated every 3-4 weeks.
There is another way of using baking soda. Pour a cup of salt down the drain, then a cup of baking soda. Boil a pot of water and pour the hot liquid over the powder.