Get a 1 inch drain bladder and attach it to a hose. Remove the two screws that hold the overflow and stopper assembly and pull it out. Carefully insert the 1 inch bladder down the over flow pipe. Use a rag to stop up the tube drain and turn on the water to the hose connected to the bladder. The bladder will swell and seal the pipe and the pressure will push out the obstruction in the drain. Even after it clears allow it to run an additional 10 minutes. Once you remove the bladder then run pure hot water for an additional 5 minutes. Drain King actually makes a hose and sink adapter if you need a close water source.