I took off and cleaned the p-trap and connecting pipes from the sink to the wall. I snaked the pipe in the wall approx 4 feet down. The sink drain pipe in the wall is about four feet to the toilet drain. I know this because I just re-did the basement last summer. The pipes connected to the toilet drain and tub drain are working fine. What happens is the p-trap fills up and the water backs up into the sink. The water in the p-trap is not going down the drain. When the water backs up into the sink it very slowly goes down. I even poured water into the wall pipe when the p-trap was off and the water went down without a problem.
Thanks