Bathtub Drain Leaking? Find the Source and Fix It
A leaking bathtub drain almost always comes from one of four places: the drain flange seal, the gasket under the tub, the overflow assembly, or a joint in the drain pipe below. Stop using the tub, run a short test to see when the water appears, and fix or call for help based on what the test shows. The sooner you act, the less chance a slow drip becomes a stained ceiling and a mold problem.
This guide walks through the test, the likely causes, what you can reasonably try yourself, what a repair usually costs, and the signs that mean it is time for a licensed plumber. We are a plumbing and HVAC company serving the Greater San Antonio area, and we would rather you understand the problem than be sold a bigger job than you need.
TL;DR
Stop using the tub right away and note when water shows up: while filling, while draining, or all the time. That timing points to the source.
A plugged-drain water test separates a drain or overflow seal leak from a pipe or supply leak.
Loose flanges and worn gaskets are the common causes, and a failed seal under the tub often needs access from below or a professional tub drain replacement.
Water coming through a ceiling, a sewage smell, or damp drywall means call a plumber now, not after the weekend.
Do not pour chemical drain cleaner into a leaking drain. It will not fix a leak and can make a weak joint worse.
Table of Contents
What to do in the first hour
Before you diagnose anything, limit the damage.
Stop using the tub and shower. Every gallon that goes down a failing drain can end up in the wall, subfloor or ceiling below.
Catch what you can. Put a bucket under a dripping ceiling spot and towels on the floor. If the ceiling is bulging with water, poke a small hole in the lowest point of the bulge over a bucket so it drains in a controlled way instead of letting the whole section fall.
Write down the timing. Plumbing guidance recommends noting whether water appears only when filling, only when draining, or continuously, because that detail helps the plumber find the source without unnecessary demolition.
Do not start pulling panels or cranking on parts blindly. The same guidance names blind tightening and ad hoc panel removal as the most common homeowner mistake. Over-tightening can crack a plastic drain body or crush a gasket.
Take photos. Date-stamped pictures of stains and wet areas help if you ever file an insurance claim.
If the water is coming from a pipe rather than the tub, for example a burst line, shut off the main and follow our guide on what to do about a burst pipe.
How a tub drain is put together
Knowing the parts makes the leak easier to place. A standard tub has two openings that lead to the same trap and waste line:
The drain flange (or shoe): the visible metal ring at the bottom of the tub. It threads into a drain body or shoe below the tub and is sealed with plumber’s putty or silicone on top, with a gasket underneath.
The gasket or washer: a rubber or fiber seal under the tub floor that keeps water from escaping around the flange.
The overflow: the slotted plate on the tub wall. It connects through a tube to the drain so excess water has somewhere to go.
The tailpiece and trap: pipe below the tub that carries water to the main drain. Joints here are slip-nut or glued connections.
Water can get out at any of those joins. The tub itself only holds water while it sits in the basin. The moment you open the drain, every seal below the tub is tested.
The two-minute test that finds the source
You can narrow the cause with water and a dry towel. The approach below follows the standard diagnostic logic described by The Spruce: create a pool and watch whether the level drops.
Test 1: Fill the tub past the overflow
Plug the drain and fill the tub to just below the overflow plate. Wait 15 to 20 minutes. If water shows up below while the tub is full and the drain is closed, suspect the overflow gasket or the overflow tube connection, since the drain itself is not carrying any flow.
Test 2: Let it drain
With the tub full, pull the plug and watch the area below. If the leak appears only while water is going down, the drain flange, the gasket under it, the tailpiece or the trap is the likely culprit.
Test 3: Run the faucet only
Run water with the drain open and a small flow. If the leak happens while water is running but stops when the flow stops, look at the faucet, spout, shower valve and the wall around them as well. A bad spout seal or cracked caulk can mimic a drain leak.
Test 4: Check the tub surround and shower door
If you have a shower, splash water on the wall and around the door frame separately from the drain. Family Handyman notes that leaks around a frame can take five minutes or longer to show up, so be patient before you rule an area out.
Reading the results
What you see | Most likely cause | Typical next step |
Leak only when water is above the overflow plate | Overflow gasket or tube connection | Replace the overflow gasket |
Leak only while draining | Flange seal, drain gasket, or tailpiece joint | Reseal the flange or replace the drain assembly |
Leak with the drain closed and tub at normal level | Cracked tub, loose flange, or failed putty seal | Inspect the flange and tub surface |
Leak while faucet runs, tub empty | Spout, valve or wall caulk | Check the supply side and caulk lines |
Constant slow dampness | Pipe joint or a hidden supply line | Professional leak detection |
Common causes of a leaking tub drain
A loose or dried-out drain flange
The flange is sealed with putty or silicone when the tub is installed. Over years the sealant dries, shrinks and cracks, and the flange can work loose from the shoe. Water then seeps around the ring and drips below. This is one of the most common causes, and in some cases a tub wrench can snug the flange back down.
A worn drain gasket
Rubber and fiber gaskets harden with age. A hard gasket no longer compresses against the tub and the drain body, so water slips past it, usually only when the tub is draining. Replacing the gasket is simple on paper, but reaching it often means getting under the tub through an access panel, or from the ceiling below.
An overflow gasket or tube problem
The overflow gasket sits behind the faceplate. When it dries out or the screws loosen, water pours through it every time the tub is filled high or someone sits down in a full tub. The overflow tube can also separate from the tee below it.
A cracked drain body or tailpiece
Older tubs may have brass drain fittings that corrode, while plastic parts can crack when someone has over-tightened them. A cracked piece cannot be sealed with putty. It needs replacement.
A failing trap or slip joint
Below the tub, slip-nut connections can loosen from vibration or movement. Water that drips from a joint is often mistaken for a drain leak but is really a trap or pipe leak.
Hidden leaks, including in slab homes
Many San Antonio homes sit on slab foundations, where a ground-floor bathroom drain runs in or under the concrete. A leak there will not show as a ceiling stain. You may see a damp floor, a musty smell, a rising water bill or even soil movement. That calls for leak detection and under-slab plumbing repair rather than a DIY gasket swap.
Why you should not wait
A drain leak is rarely a one-time event. It repeats every time the tub is used, which means the same materials get wet over and over.
Mold can start fast. FEMA’s guidance on mold and mildew says mold can begin growing within 24 to 48 hours of water exposure, and porous materials like drywall, carpet and wood are at highest risk of structural damage.
Structure takes the hit. Persistent moisture can warp subflooring, delaminate sheathing and rot framing, especially in wood-frame houses. If the leak is above a finished room, you may also be dealing with a sagging ceiling. Once the plumbing is repaired and the area is dry, a drywall contractor can handle ceiling repair and texture matching. Hardwood floors react quickly as well, and water damage to hardwood floors is something you want to catch within days.
Drain water is not clean water. A drain leak carries wastewater. HUD’s inspection standard treats sewage system leaks as a high-risk health issue and says deficiencies such as puddles, strong odors or stained materials call for attention within 24 hours. If you smell sewage in the bathroom, read our guide on what causes a sewer smell in a bathroom and treat it as urgent.
Humidity gets worse. Ongoing leaks raise moisture in the house. If you are noticing a persistent damp feel, our piece on high indoor humidity and leaks explains how to tell where it is coming from.
What you can try yourself, and what you should not
We prioritize repair over replacement, and plenty of small leaks can be fixed cheaply. But a tub drain sits in a spot where mistakes get expensive, so here is an honest split.
Reasonable DIY steps if you are comfortable with tools
Re-caulk or replace the overflow faceplate gasket. Remove the screws, swap the gasket, and reseat the plate. If the leak appears only at high water levels, this is often the fix.
Tighten a loose flange with a tub drain wrench. Hand-tight plus a snug final turn is the goal, not full force. If the flange spins freely or the threads feel stripped, stop.
Reseal the flange with fresh plumber’s putty or silicone. This requires removing the flange, cleaning off old sealant and setting it again with a new gasket. A single leftover bit of old putty can cause a repeat leak.
Tighten an accessible slip nut on a visible trap joint, by hand or with gentle pliers.
If you have already reapplied putty more than once and the leak keeps coming back, the problem is probably the gasket, a worn thread or a cracked part, not the sealant.
Do not do these
Do not use chemical drain cleaner or a plunger on a leaking drain. Experts warn that chemicals and aggressive plunging can weaken aging PVC joints or corrode old pipe, turning a small drip into ceiling damage.
Do not cut into drywall or a ceiling blindly. Opening the wrong spot adds repair cost and can hide the real source.
Do not seal over a leak with caulk and call it fixed. Caulk on the outside of the tub does not repair a failed gasket underneath.
Do not keep bathing while you wait. Running the tub for a few weeks is how a small leak becomes a rotted floor.
When to call a plumber
Call a licensed plumber if any of these apply:
Water is dripping through a ceiling or staining a wall below the bathroom.
You cannot reach the drain from beneath the tub, and there is no access panel.
The flange or drain body is cracked, corroded or stripped.
A repair you made has leaked again.
You notice sewage odor, slow drains or gurgling along with the leak.
The bathroom is on a slab and you see damp flooring or unexplained water bill increases.
The leak could be from a supply line rather than a drain, and you cannot tell which.
The Plumber.org.uk guide makes a point we agree with: an unknown source is a valid report. You do not need to name the exact failed part when you call. A clear description of when the water appears, where you see it and how long it has been happening is the best information you can hand over.
What a professional visit looks like
A good plumber will start by asking about the timing, then test the tub the way we described above. From there, the tech finds the cause before quoting a repair. At Texas Comfort Crew, we explain what we found, show you your options, and let you decide. We do not push a full replacement when a gasket, a reseal or a section of pipe will do.
What a tub drain repair costs
Costs vary a lot with access, pipe material and whether walls or ceilings need to be opened. For context, Angi’s 2026 figures put bathtub or shower drain replacement between $500 and $1,020 for most homeowners, with a national average of $700. The same source says water damage, drywall and related repairs can add $1,350 to $6,100.
The pattern matters more than the numbers: the plumbing repair is usually the smaller bill, and the damage from waiting is the bigger one. We do not publish flat prices, because a drain that is easy to reach from a panel is a different job than one buried behind a finished ceiling or under a slab. We give you the price and the options after we look at the actual problem.
Our perspective: fix the seal, not the whole bathroom
Homeowners call us after a stain shows up on the ceiling or after a second putty job fails, and they often expect to hear that the tub needs to come out. Most of the time it does not. When we look at a leaking tub drain, we want to answer three questions before we recommend anything: where does the water actually come from, what is the least invasive repair that will last, and what will it cost to do it right versus doing it again in a year.
That is why we lean toward repair. A worn gasket, a loose flange, or a failed overflow seal is a contained problem, and it should be fixed as one. If a part is cracked or corroded and can no longer hold a seal, we will say so and explain why replacement is the better choice. Either way, you should understand the reason in plain words and keep the final say.
The other thing we see is how many homeowners wait because the drip seems small. In our experience, a bathroom leak is not a problem that improves with time. If you take only one thing from this article, let it be this: stop using the tub, write down when the water shows up, and get it looked at before the ceiling tells you the story.
— Dan Patino
Get a leaking tub drain looked at
If your tub drain is leaking and you are in the Greater San Antonio area, our team handles plumbing repairs, drains and sewer lines for homeowners, including diagnosing where a leak starts and explaining each option before any work begins. If you suspect the water is traveling somewhere you cannot see, ask about leak detection. You can also check our service areas to confirm we cover your neighborhood.
Preventing the next leak
Check the caulk and overflow plate twice a year. Look for gaps, soft spots or stains.
Use a hair catcher. Clogs push people toward harsh chemicals and aggressive plunging, which stress old joints.
Watch for early signs. A faint musty smell, a damp spot on the ceiling below, or a bathroom floor that feels soft near the tub deserve attention before they grow.
Follow a seasonal routine. Our plumbing maintenance checklist covers the small checks that catch leaks while they are still cheap to fix.
Know your shutoff. If a leak turns into a pipe failure, knowing where the main is can save thousands of dollars.
FAQ
How do I stop my bathtub drain from leaking?
First stop using the tub, then run the fill and drain tests to learn whether the overflow, the flange or a pipe joint is leaking. Overflow and flange leaks can sometimes be fixed by replacing the gasket or resealing with fresh putty or silicone. If the part is cracked, corroded or out of reach, have a plumber handle it.
Can a tub drain be replaced without removing the tub?
Usually yes. Most drain assemblies can be replaced from above using a drain removal tool, and from below through an access panel or opening. The main limit is access to the trap and waste pipe. If there is no panel and the plumbing is behind a finished wall or ceiling, a plumber may need to open a small section.
How much does it cost to fix a leaking tub drain?
It depends on the cause and access. One national source puts drain replacement at $500 to $1,020 for most homeowners, while a simple gasket or reseal can cost less. Ceiling and drywall repair is a separate cost.
Why is my bathtub leaking into the room below?
The leak is most likely at the drain gasket, the overflow connection or a trap joint, though a spout or valve leak can produce the same stain. Water can travel along joists before it shows up, so the stain is not always directly under the problem. Stop using the tub and have the source confirmed before repairing the ceiling.
Is a leaking tub drain an emergency?
Treat it as urgent if water is coming through the ceiling, you smell sewage, or the area stays wet. Drain leaks carry wastewater, and mold can begin within 24 to 48 hours of moisture exposure. A slow drip with no staining still needs attention soon, but you can usually schedule it within a day or two.
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