A soggy sink cabinet has exactly three suspects: the drain assembly (leaks when water goes down), the supply lines (leak all the time), or the faucet base (leaks when the faucet runs). One roll of paper towels and ten minutes of detective work identifies the guilty party — and all three fixes are firmly DIY.
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Scan It FreeEmpty the cabinet, towel it dry, and lay fresh paper towels flat under every joint. Now you have a leak detector.
Plug the sink, run water into the basin. Towels wet under the supply valves or lines = supply-side leak (constant pressure). Wet at the faucet's underside = base/O-ring leak.
Pull the plug and let it all drain at once. Fresh drips at the P-trap joints, the sink strainer, or the disposal connections = drain-side leak. Note exactly which joint the towel caught.
P-trap slip nuts: snug by hand plus a quarter turn. Still weeping? Disassemble, check the washer is seated flat (not folded), the trap aligned without side-load. Strainer leaks: re-bed the strainer in fresh plumber's putty.
Compression nuts at the valve: snug gently — overtightening splits ferrules. Weeping braided lines or crusty valves: replace the line ($8) or shut the main and swap the valve. Braided stainless lines are cheap insurance; rubber-only lines are on borrowed time.
Water rings around the faucet on the countertop drain along the tailpieces below. Most spouts pull up after a collar unscrews — replace the O-rings beneath (scan the faucet with SpotFix AI to match the O-ring kit for your model).
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