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The Drain and the Overflow

A bathtub has two openings, and the one people forget about is the one that leaks into the floor without ever dripping where you can see it.

Quick answer

The overflow gasket fails silently. Water runs down the outside of the tub and into the floor while everything above it looks normal, so the damage shows up some distance from its cause. It is told apart from a drain leak by when the water appears.

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Two openings, two failures

The drain is at the bottom and carries water away. The overflow is the opening near the rim, connected to the same waste by a pipe behind the tub, with a gasket sealing it to the tub wall.

A drain leak shows up underneath. An overflow leak shows up nowhere obvious, because the water runs down the outside of the tub and into the floor.

How to tell which

Timing and water level. A leak that appears when the tub is full or when somebody lies back in it — raising the level to the overflow — points at the overflow. A leak when the tub drains points at the waste below.

A leak that only happens when the shower is running and the tub is empty is usually neither: that is the enclosure or the seal at the rim rather than the plumbing.

Why it matters more than a dripping tap

Because the water goes into the structure rather than into the drain. Soft subfloor under a tub is most often this fault, found years after it started, and the repair is then the floor as well as the gasket.

What to ask

Whether the overflow gasket was checked, and whether anything under the tub is damp. On an older fixture both are quick to establish and both are routinely skipped.

Changing a tub is mostly about what is behind it.Tell us what you want done and we will route you to a contractor in your area, found from your ZIP code, who can look at the wall and the floor before quoting. No charge to you, and we will not ask you why. Anything else needing a plumber is fine to bring up while we have you.

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