Overflow Tube - Toilet Tank Refill and Overflow Guide

An overflow tube is the vertical tube inside a toilet tank that prevents overfilling and provides the refill path that restores water to the bowl after each flush.

What It Is

The overflow tube is part of the toilet flush valve assembly. If the fill valve does not shut off correctly, rising water spills into the top of the tube instead of running onto the bathroom floor. During normal flushing, the refill tube also directs a small stream into the overflow tube so the bowl refills to the proper water level.

Because it serves both overflow protection and bowl refill, a damaged tube can create several symptoms at once. A crack can cause phantom refilling, while an improperly positioned refill tube can leave the bowl underfilled after each flush.

Where It Is Used

Overflow tubes are used inside standard gravity-flush toilet tanks as part of the flush valve assembly. They sit in the center or near-center of the tank and connect directly to the flapper or canister-style flush mechanism.

How to Identify One

The overflow tube is the open vertical tube visible inside the tank above the flush valve seat. A small refill hose from the fill valve clips to the top of it. The top of the tube sits below the tank lever opening and below the top edge of the tank itself.

Replacement

Replacement is needed when the tube cracks, the top breaks off, or the entire flush valve assembly is leaking or worn out. Because the tube is usually molded into the flush valve, repair often means replacing the full flush valve rather than the tube alone. That requires shutting off the water, draining the tank, and removing the tank in many toilet designs.