Sink Repair
Under-sink leaks obey a simple law: water appears either when the faucet runs, when the basin drains, or all the time, and each schedule names its own suspects. Runs-only leaks live on the pressurized supply side. Drains-only leaks live in the flange, tailpiece, pop-up or trap. Always-wet points at a connection weeping under standing pressure. One towel and two tests sort the entire cabinet.
Signs You Need This Service
Reading the puddle's schedule:
- Wet only while the faucet runs. Supply side: connectors, stop valves, or the faucet's underside. Pressurized joints announce wear while water moves through them.
- Wet only when the basin drains. Drain side: flange seal, tailpiece joint, pop-up assembly or P-trap. Gravity's path leaks exactly when it carries water.
- Wet regardless of use. A stop valve stem or connector weeping under constant pressure: the smallest and steadiest leaks, and the ones that ruin cabinets during vacations.
- Odor without visible water. A trap problem in another sense: a compromised seal or biofilm buildup letting smell past; occasionally a dried trap in an unused sink.
- The rocking or loose stack. Slip nuts and fittings backed off by years of touch: a leak in rehearsal, correctable before opening night.
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This page covers the sink's plumbing: connections, the drain stack, the trap, the basin's interfaces. The faucet's own mechanism has its dedicated repair page, a chronically slow drain routes to drain cleaning once hardware is acquitted, and a cracked basin moves the conversation to the installation page. What lives here is the cabinet's puddle and its short list.
How a Plumber Diagnoses the Problem
The two-test sequence:
- Dry everything, then run. Cabinet dried, faucet run without plugging the basin. New moisture now convicts the supply side, traced joint by joint to the source.
- Fill and release. Basin filled and drained hard: the full-flow test that exposes flange, tailpiece and trap failures which a trickle never provokes.
- Repair by component. The drain stack is built of serviceable parts: pop-ups rebuild, traps and tailpieces replace with fresh washers, flanges reset with new putty. Component repair, not fixture drama.
- Know the neighbors. Faucet-mechanism faults route to the faucet page, persistent slow drainage to drain cleaning, hidden wall moisture to leak detection. The cabinet diagnosis includes knowing what does not belong to it.
Frequently Asked Questions
Why is my sink leaking underneath?
One of three schedules: supply-side joints leak while the faucet runs, drain-side seals leak while the basin empties, and constant-pressure weeps leak all the time. The dry-and-test sequence sorts them in minutes, and it beats replacing parts on a guess by exactly the cost of the wrong parts.
Why does it leak only when water drains?
Because the failed seal lives in gravity's path: the drain flange, tailpiece, pop-up gasket or trap joint see water only during drainage. The fill-and-release test reproduces it on command, and the fix is component-level: fresh washers, a reset flange, a rebuilt pop-up.
Can a P-trap or pop-up be repaired, or do they need replacing?
Both are designed for service: traps disassemble by hand for cleaning and re-washering, and replacement costs little when threads or walls have worn; pop-up assemblies rebuild or swap in minutes. These are the consumable joints of the sink world. Repair is the default, not the exception.
Is a slow sink a repair problem or a clog?
Usually a clog, buildup in the trap zone, which is drain-cleaning territory. It becomes a repair matter when hardware causes it: a misadjusted pop-up sitting too low, a deformed trap, a flange obstruction. The visit checks the hardware first because that answer is faster, then routes honestly.
When should the sink itself be replaced instead?
When the basin is the problem: cracks, chips through the finish at the drain, mounting failures the fixture cannot recover from. Connection and drain-stack leaks almost never justify a new sink. The installation page owns the swap when the verdict genuinely lands there.
Sort the Cabinet Leak
Tell us the puddle's schedule (with running water, with draining, or always) and what is connected under there. The two tests name the component, and most sink repairs close in one visit.
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