Pour baking soda into the drain followed by vinegar. It will foam up and clean the drain, deoderizing in the process. Worth a try.

I think you're supposed to chase that baking soda and vinegar with some very hot (boiling?) water to finish clearing it out.

Have used the baking soda and vinegar for years, I have a septic tank. Works perfect with or with out the addition of the hot water.

SAVED MY LIFE!!!
I had a smelly sink drain (I thought) and I looked up how to fix it. I did the baking soda and water and went to turn on the stove to boil the hot water and poof! the other burner started.... It wasent a smelly sink drain but gas leaking from a stove nob that had been accedentally turned...The stove and sink are right next to each other and it was gas that I was smelling (not recognizing it as gas because I had cleaned the counter a few minutes earlier and was also smelling the cleanser)...Your advice literally saved my life...If I hadent went to boil the water I would not have found out about the gas leak....THANK YOU SOOO MUCH!!!!