How do I make a DIY solution to clear a slow flowing drain?

Pour a cup of baking soda in drain, and 2 cups,of vinegar. Let it sit awhile then rinse.

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.

Baking soda and vinegar.

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1/2 box of baking soda down the drain take out any water you can with a sponge or cloth then pour white vinegar 1 cup let it sit 20 min then pour boiling water after it

If its a bathroom drain, I would get a drain snake at the Dollar Tree or hardware store and clean all the hair and gunk out.

Use baking soda and vinegar and then rinse with hot water.

Have you tried pouring lots of BOILING water down the drain?