I got a similar situation with my washroom sink. the ********** who lived here (apparently my neighbour now) left some **** in the sink. I didn't move in for a while so I didn't notice it.
Few days after i notice some ****, hard to see just near the top of the drain hole. I jab at it with a knife and it goes down. Water was draining better, but then it's still not good.
How should I fix? snake that ****? i heard there is like some air pumps and liquid that you pour and it dissolves all the junk stuck in there.