How to Unclog a Drain with a Plunger
Repeat Step 4 but this time, pull up sharply to release the suction.
Hopefully, when you release the suction on the drain the clog will be dislodged releasing some of the water. If there’s no change, repeat Steps 3 and 4 until the water begins to drain.
If you've tried these steps a couple of times with no progress, it's time to pull out the plumber's snake.