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.
This just started a few weeks ago. When water runs from my 1/4 sink into the drain, it seems to back up and leak out of the pipe. This never happens with my 3/4 sin...
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Here are instructions https://www.hometalk.com/diy/repair/plumbing/unclog-drains-without-plunging-39466041?expand_all_questions=1
Unclog Drains Without Plunging
Unclog?
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.