I usually work it with a plunger or try it with a long stick. Sometimes it works just fine, but most of the time, it doesn’t help in anyway. I’ve recently tried how to snake the drain pipe and seems quite effective and efficient. Have you tried snakes before? If so share the experience, might help many.
Usage of snake was showed to me by Green City Plumber Service http://www.greencityplumber.ca/ agent who came to unclog our drainage.