My kitchen sink leaks into my basement. The floor of my kitchen sink is not wet. The water leaks into the basement when I drain the water. I conducted a test, it does not leak from the water lines.

Track the moisture back to its highest point. That will be the source of the leak. Let me know exactly what you find and what fitting's leaking Good luck, Tom

Lay toilet paper covering the entire floor under your sink. Fill the sink and drain it, if there is a leak on the interior side of the wall you'll see it immediately. The leak could be just inside the wall where the horizontal pipe connects to the drain pipe. It could also be a section of the drain pipe. Answers Tom and my questions please