Try this: Pour boiling water down the drain. Then add a half cup of baking soda and let it sit for a minute. Pour a cup of vinegar and a cup of hot water down the drain. Cover loosely and let it sit for 10-15 minutes. Pour another pot of boiling water down the drain to flush out the clog.
Hi Maria. Here are some posts on how to do it... https://www.hometalk.com/search/posts?filter=unclog%20sink
We've had good luck using an unclogging bladder. They're pretty inexpensive and they use pressure to flush out the clog
I would buy a drain snake and chuck it into my cordless drill. They can be used for years on any size drain.
Remove as much as possible with a snake or drain cleaning tool. Pour ½ cup baking soda then ½ cup white vinegar in the drain and cover, letting sit for 20 minutes. Boil water, remove cover, and pour water down the drain. You may have to repeat the process.