Check the "P-Trap" - How to Unclog a Drain in 6 Steps - Bob Vila
Check the "P-Trap"
My first line of defense for unclogging a stopped-up drain is to check the "p-trap"—the elbow-shaped pipe under the sink. Be sure to put a bucket under the pipe before removing it. Unscrew the connectors securing the pipe to the sink drain and the wall, and check for obstructions. If the p-trap isn’t clogged, there’s probably GUNK inside the drain. Brace yourself!