Cut a lemon or an orange in half then turn on the garbage disposal.
Always make sure that you use the drains often enough to keep water in the trap. Otherwise you will get sewer gases comming into your home. Like extra bathroom toilets,sinks and showers.
Draino - and stop letting crap go down the drain to rot!!
drain cleaner first, cuz there is probably something down there stuck making it stink, then try lemon juice. lemon juice gets everything out. If u have a garabge disposal that smells, take a lemon slice and run it thru the disposal with hot hot water. they also have these little balls at bed bath and beyond for clealning a disposal.
Food is down there. Try bleach, drain cleaner or baking soda. Flood the pipes with water to flush food out.
Dry caustic soda, put about 300 grams in the drain and flush with boiling water.
O, and stand back a bit.
You can get caustic soda at your building material store.
After cleaning your sink with a normal cleaner, try clorox. Empty one cup full down the drain and let it sit after a while rinse. If that does not work lemon juice is a sure cure.