Almost every sink problem traces to one of four things: the drain assembly under the bowl, the shut-off valves and supply lines feeding the faucet, the faucet itself, or the branch drain line running back into the wall. Water in the cabinet is nearly always a trap, a tailpiece or a valve. A slow drain is nearly always the trap or the branch line. A licensed plumber can tell which it is in a single visit, with the cabinet open and the water running.
What sink repair covers — the four systems under every sink
A sink looks like one fixture. Underneath it is four separate systems that fail for different reasons and on different schedules, and in Northern Virginia houses they fail in a fairly predictable order. Knowing which one you are looking at is most of the diagnosis:
- The drain assembly
- Basket strainer or pop-up, tailpiece, P-trap and trap adapter. This is slip-joint work, it is the part most often assembled wrong, and it is where most under-cabinet water comes from.
- The shut-off valves and supply lines
- The two stops on the wall or cabinet floor, and the braided lines running up to the faucet. These are the highest-failure parts in the whole house, and they fail quietly.
- The faucet
- Cartridges, seats, aerators, spray heads and mounting hardware. Sometimes a repair, sometimes not — see faucet repair and replacement.
- The branch drain line
- The pipe in the wall or floor that carries the waste away, along with the vent that lets it drain. This is where clogs live, and where a missing cleanout turns a ten-minute job into an hour of opening up a cabinet.
We open the cabinet, run the water, and look at all four before touching anything — because replacing a faucet on top of a failing valve just means a second visit.
Why a sink leaks under the cabinet
Under-cabinet water has a short list of causes, and they look different once you know what to look for:
- Slip-joint failure at the P-trap. Nuts back off, washers flatten, and metal slip nuts corrode. We have pulled traps where the metal nuts had corroded through and the joint was simply weeping, and one where a previous repair consisted of electrical tape wrapped around a cracked trap.
- A rusted-out tailpiece or flange. On older assemblies the metal flanged tailpiece corrodes from the inside, and by the time it shows it has a hole through the nut.
- A dripping shut-off valve. A stop that drips a few drops an hour will not flood a cabinet, but it will rot the cabinet base and the subfloor under it. We have replaced cabinet bottoms that failed long before anyone noticed the valve.
- A faucet leaking from the base down into the cabinet. Water runs down the shank and appears at the bottom, which is why people are certain the drain is the problem when it is not.
- Piping assembled wrong. Traps installed backwards, glued joints where slip joints belong, trap adapters pointing the wrong way, and drain lines that step down in size and back up again. All of these hold water, and all of them eventually leak.
There is also the leak that is not a leak. On more than one call we have run every fixture in a kitchen for several minutes, inspected the faucet, drain, waste pipe and valves, and found nothing wrong — while a house-wide valve check found a dozen stops leaking elsewhere. Finding nothing at the sink is a legitimate result, and we say so.
Why a sink drains slowly or backs up
A slow sink is a partial blockage. Where it sits determines the fix:
- In the trap. Hair, soap and grease collect at the bottom of the P-trap. Dropping the trap and cleaning it is straightforward, and on a bathroom sink a clogged trap is the single most common cause of a slow drain we find.
- In the branch line. If the trap is clear and the line still runs slow, the blockage is in the pipe behind the wall. That needs cabling, and afterwards a drain treatment so the line does not re-load immediately.
- In the vent. A sink that gurgles, or that drains fine alone and badly when another fixture runs, is usually a venting problem rather than a blockage. Air admittance vents fail, and older houses have fixtures that were tied together improperly by someone who was in a hurry.
- Further downstream. When more than one fixture is slow at the same time, the problem is the main line, not the sink — that is drain cleaning or, in the worst case, a sewer line issue.
Chemical drain cleaner rarely helps and often makes the visit harder. We have arrived to find a cabinet full of standing caustic waste water that had to be dealt with before anyone could open a joint.
Shut-off valves: the part of a sink repair nobody thinks about
The stops under a sink are the parts we replace more than anything else in this trade, and they matter far beyond the sink they serve. A valve that will not turn is what stands between you and shutting the water off when something bursts.
Multi-turn stops disintegrate internally. We have changed valves that had no washer left inside at all, and traced a running toilet to debris from a disintegrating valve washer clogging the fill valve. We have found stops that had broken apart internally while still looking fine from the outside, with the debris traveling up and blocking the faucet. We have found one buried in spray foam where nobody could reach it, and another that came apart in a bystander's hand during a visit and flooded a kitchen.
Because of that, a valve check at every fixture in the house is standard on our plumbing calls. It is not unusual to find five, eight or a dozen stops that need replacing in one house — and when we do, the cause is usually upstream. Static water pressure above the code limit destroys valves, supply lines and faucets everywhere at once. We gauge the incoming pressure on the call; if the pressure reducing valve has failed, see water pressure, PRVs and shut-off valves.
When we replace stops we fit quarter-turn valves and metal braided supply lines, and we drain the system down first rather than working against live water.
Kitchen sink or bathroom sink — where to go next
The two are genuinely different jobs. A kitchen sink carries grease, food waste, a dishwasher discharge and usually a disposal, so its failures are drain-line failures. A bathroom sink carries hair and soap into a smaller trap, and its failures are trap, valve and faucet failures.
| Sink | What usually goes wrong | Where to read more |
|---|---|---|
| Kitchen sink | Grease-loaded branch line, no cleanout, disposal and dishwasher tie-ins, failed stops | Kitchen sink repair |
| Bathroom or vanity sink | Clogged trap, corroded slip nuts, dripping stops, vanity and pedestal replacement | Bathroom sink repair |
| Disposal side of a kitchen sink | Seized motor, leaking housing, loose drain flange | Garbage disposal repair |
| Utility, slop and laundry sinks | Failed stops and supply lines, drain tie-ins shared with the washer | Handled the same way — call it in as a sink repair |
Sink installation: drop-in, undermount, pedestal and vanity
Setting a new sink is more than the bowl. A proper installation means new stops and supply lines rather than reusing tired ones, a drain assembly built with a cleanout where the line allows it, and the sink itself mechanically supported.
Undermount sinks are the ones that come back. They are held to the underside of the counter by adhesive, and when that bond ages the sink drops away with no mechanical support underneath. Resetting one properly means disconnecting the drain piping, cleaning both the sink rim and the underside of the counter, dry-fitting to confirm the fit, bedding it in a waterproof adhesive, adding wood blocking for support, and then leaving it unused for the full cure time before anything is reconnected.
Pedestal sinks need the baseboard behind them removed to get the pedestal out, and the wall behind repaired and painted before the new one goes in. Vanity work usually turns up drywall damage behind the old unit that has to be patched and sanded ready for paint. We include that in the scope rather than leaving you with a hole.
Do you need a permit for sink plumbing work in Virginia?
Changing a faucet, a trap or a set of shut-off valves does not require a permit. Cutting into supply or waste piping, running new water or drain lines to a sink location, replacing a pressure reducing valve or adding an outside connection does — and we pull and process those permits ourselves.
Work is performed to the Virginia building code and the job is not closed out until the county inspection passes. Permit and permit processing fees are written into the contract before work starts. Where we cut copper water piping we restore the bonding across the gap, because in a lot of these houses the metal piping is part of the grounding path.
Where a sink has to be added somewhere there was no plumbing at all, the work is a rough-in: supply tapped from the nearest accessible lines, a waste line tied into an existing drain where the fall allows, and a conventional vent — or an air admittance vent only where code allows one.
What a sink repair visit includes
- Confirm the symptom with the water running. Fill the bowl and let it go, rather than trusting a trickle test.
- Open the cabinet and inspect all four systems. Drain assembly, stops and supply lines, faucet, and the piping going back into the wall.
- Gauge the incoming water pressure. Standard on our plumbing calls, because high static pressure is behind an enormous share of the valve and faucet failures we are called out for.
- Check the rest of the house. Every stop at every fixture, because they age together and they fail together.
- Show you what was found. Photographs where the problem is inside a wall or a ceiling, and a plain explanation of what is repairable and what is not.
- Drain the system down and do the work, then refill, run the fixture and test every joint before the cabinet gets closed up.
If the drain line has been slow for a while, we snake it and treat it rather than clearing just enough to make the symptom go away for a fortnight.
What sink repair costs, and how we price it
We do not quote sink work by phone and we do not publish numbers. Two sinks that look identical from above can differ by a corroded galvanized branch line, a missing cleanout, stops that have to be cut out rather than turned off, a faucet whose parts are no longer made, or a cabinet base that has quietly rotted through underneath. A number given sight-unseen is either padded for the unknowns or it is going to change.
An estimator comes to the property, opens the cabinet, and gives you a written price for the work in front of him before anything starts. That is how every job at this company has been priced since 1999.