Snaked it out at the main under the sink and put it back together ,put small amount of water in sink and it did not drain. I lossened the flap between the two oipes and it drained. But not into the ground. Is there a vacuam that has to occure for it to drain?

Would this be a kitchen or a bathroom sink? You loosened what flap? Please give us more details. Tom

It is my sink where the washer drains in the basement the flap I referd to is on the pvc pipe that connects to the main pipe going into the ground. I have also checked the floor drain in the basement and poured water into it and it draines real slow the rest of the drains in the house seem to be OK . I tried baking powder salt and vinegar solution in the sink to no avail when I loosen the pvc connector to the main pipe I don't see any back up of water into the ground ,just the water I poured into the sink draining out HELP Please

Let's see if I have this correct.
You have a slop sink in your basement and a check valve, (the flap?) on the drain. I( I wonder why) and both the sink and the floor drain drains slow.

I lossened the flap between the two oipes and it drained. But not into the ground. In don't understand this part at all. Can you explain it farther? Sorry! I guess it's just me this morning. Tom