Direct answer: If the leak only shows up when the tub water gets high or when water is poured into the overflow opening, the bathtub overflow gasket is the likely problem. If it leaks with a shallow tub or while draining, look at the bathtub drain or waste-and-overflow connections first.
Most likely: Most often, the bathtub overflow gasket has shifted, flattened out, or was never compressed evenly behind the overflow plate.
Start by proving when the leak happens. A true overflow-gasket leak is usually quiet until the water level reaches the overflow opening. Reality check: a drip showing up downstairs is often several inches away from the actual leak point. Common wrong move: replacing the whole drain assembly before doing a simple fill test at the overflow.
Don’t start with: Do not start by caulking around the overflow plate face. That usually hides the leak path instead of fixing the seal behind it.
No drip with a shallow bath, but water shows up below or behind the tub once the water level reaches the overflow opening.
Start here: Start with a controlled overflow test. This is the strongest sign the bathtub overflow gasket is leaking.
A helper pours water directly into the overflow and you see moisture at the back of the tub or through an access opening.
Start here: Check for a loose overflow plate, a crooked gasket, or a gap between the overflow elbow and the tub wall.
The leak starts after you pull the stopper, even if the water level never reached the overflow.
Start here: This points away from the overflow gasket and more toward the bathtub drain, waste shoe, or drain piping.
You see water after showering, even without filling the tub high enough to touch the overflow.
Start here: Look for a tub spout, valve wall, or surround leak before blaming the overflow gasket.
This is the classic cause when the leak appears only once water reaches the overflow opening.
Quick check: Remove the overflow plate and look for a gasket that is hard, misshapen, slipping downward, or not centered around the overflow elbow.
If the plate is not pulling the overflow elbow snug to the tub, the gasket cannot seal evenly.
Quick check: Gently snug the screws by hand. If one side was loose and the leak improves, the seal was not being compressed properly.
A drain-side leak often gets blamed on the overflow because the drip shows up in the same general area below the tub.
Quick check: Fill the tub only a few inches and let it sit. If it stays dry until you drain it, the problem is likely lower at the drain path.
Shower spray can send water behind the wall and make it look like the overflow is leaking.
Quick check: Run the shower without filling the tub. If the area gets wet, the overflow gasket is probably not the main issue.
You want the first wet condition, not the final drip location. That separates overflow leaks from drain and wall leaks fast.
Next move: If the leak appears only when water reaches the overflow opening, stay on the overflow-gasket path. If the leak starts during draining or during shower use, the overflow gasket is probably not your main problem.
What to conclude: Timing tells you more than the drip spot. Overflow leaks are level-related; drain leaks are flow-related; wall leaks often show during shower spray.
A loose plate or shifted gasket is common and can sometimes be corrected without replacing parts.
Next move: If the leak stops after the plate is reseated and tightened evenly, the gasket was likely misaligned rather than failed. If the gasket is brittle, torn, permanently flattened, or still leaks after reseating, replacement is the next likely fix.
What to conclude: The overflow seal depends on even pressure. A good gasket can leak if it is cocked sideways or if the plate was tightened unevenly.
A lot of homeowners replace the overflow gasket when the real leak is lower at the drain shoe or waste connection.
Next move: If the leak shows only during draining, shift to the bathtub drain leak path instead of replacing the overflow gasket. If the drain area stays dry and the leak returns only at the overflow level, the overflow gasket remains the best-supported fix.
Once the leak pattern is confirmed, a new gasket and proper alignment usually solve it.
Next move: If the area stays dry at overflow level, the repair is complete. If a new gasket still leaks, the overflow elbow may be distorted, the tub surface may be damaged, or the leak may be coming from another branch nearby.
You want one clean answer before patching drywall or buttoning up the access opening.
A good result: If all three tests stay dry, reinstall the access cover and monitor the area over the next few uses.
If not: If water still appears, move to a drain, wall-entry, or cracked-tub diagnosis instead of continuing to swap overflow parts.
What to conclude: A dry retest confirms the repair. A repeated leak after a proper gasket replacement means the problem is elsewhere or the tub surface itself is compromised.
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Not as the real fix. The water seal is the bathtub overflow gasket behind the tub wall. Caulk on the face may slow visible seepage for a while, but it usually traps the problem and makes later diagnosis messier.
Watch when the leak starts. If it leaks only when the water level reaches the overflow opening, the overflow gasket is the likely culprit. If it leaks while the tub is draining, the bathtub drain or waste shoe is more likely.
Not always. Many tubs let you remove the overflow plate from the front and pull the overflow elbow forward enough to change the gasket. If the assembly drops back or there is very little movement, rear access may be needed.
Water travels along framing, pipes, and the underside of the tub before it finally drips. That is why the first wet point matters more than the final drip spot.
Then the problem may be a crooked overflow elbow, a damaged tub surface at the opening, a bad overflow plate fit, or a leak from the drain or wall side that only shows up during the same test. At that point, stop guessing and trace the first wet point again.