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What is a Bathtub Overflow Drain? 2024 Guide

Bathtub overflow drains provide a great asset to any bathroom, helping to prevent flooding when filling the bathtub. Although it can be a bit more complicated than installing a regular drain, we will look at all the benefits an overflow drain can bring and most importantly, how it works. 

What is an overflow drain?

The point of an overflow drain is to collect the excess water for your bathtub or faucet. The drain collects the water, preventing it from overflowing if you accidentally leave it on. An overflow drain can also help to keep a minimal level of water in a bathtub-as long as the overflow drain is kept in the right position, it will drain water, but keep the existing level, ensuring that you have a consistent level of water when you turn the water on before your bath. 

Why is the overflow drain important

As stated previously, an overflow drain helps to ensure that your bathtub does not overflow if you leave the faucet on. This is important if you don’t want to wait by your bathtub while it slowly fills with water for your bath. Beyond just creature comfort, it also ensures that water won’t spill out and flood your bathroom if the faucet is left running. 

Types of Overflow Drains 

With overflow drains, there are two primary types available: Traditional and Integral. Which one you have in your home will largely depend on the age of your house or bathtub. 


A traditional overflow consists of a hole cut into the tub to accommodate a drain that installs on the inside and outside walls which collect excess water and sends it down a tub drain to a P-trap. This style is perhaps the most common in older homes and requires some flexibility in cutting and installing the pipe system. 


An Integral overflow is designed a little differently than the traditional style. Whereas the traditional overflow is made with an exterior pipe and drain system, an integral overflow is similar to a sink overflow. An opening is cut along the interior of the bathtub and the excess water is then diverted between the walls of the tub drain. This style is popular for those that don’t want to deal with exposed piping as the overflow channel is built in the tub’s inner wall. 

Parts of a overflow drain:

  • Cover
  • Overflow washer
  • Cover Screws
  • Overflow Pipe
  • Overflow Trap
  • Waste Arm
  • Stopper
  • Rubber Gasket
  • Drain Elbow

How does the overflow drain work?

An overflow drain may seem complicated at first, but the actual mechanics are fairly straightforward. Here is how an overflow drain works:

  1. Water runs through the main drain
  2. If the main drain is plugged or sealed by a mechanical stopper, water will begin to build up.
  3. When the main drain fills, water will begin to reach the overflow stopper instead, allowing it to drain
  4. As long as there is decent pipe flow, your overflow will prevent water from building beyond a certain point, preventing your bathtub from overflowing. 
  5. The overflow drain has two parts: an overflow drain and a trap. The trap locks and unlocks the drain, allowing water to flow in and out. 

Overflow drain diagram

An overflow drain consists of an overflow cover which protects the top of the overflow and usually contains the switch that engages and disengages the trap. The washer seals the top of the overflow. This leads to the bottom of the drain, which contains a separate cover that is sealed by a gasket and a stopper.

overflow drain diagram.

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Does a bathtub need to have an overflow drain? 

Depending on the style of bathtub and its use, an overflow drain is not always necessary. If your bathtub is a shower/bathtub combo or a smaller model, then it isn’t necessary. Installing an overflow drain is also a bit more involved than installing a standard drain. That being said, it is essentially a safety precaution and is recommended for all bathtubs just to prevent overflow and flooding if you ever decide to fill your bathtub and walk away. 

Issues that can occur with a problematic overflow drain

There are a few issues that can occur with an overflow drain. Please keep in mind that while an overflow drain is a great addition, it is also installing a secondary pipe system that can corrode or leak.  


Clogs can easily occur in any household that sees extensive use. Most commonly, hair and other debris cause clogs, which ultimately disrupt water flow and create obstructions in your piping. Clogs result in lower water pressure over time and may lead to damages in the future if left unattended. This is why it’s important to clean or repair your clogged pipes annually. 


Leaks can occur over time due to the natural erosion of the pipe material. Leaks will result in lower water pressure and, eventually, water damage to your other pipes and housing material, so it is best to inspect your plumbing regularly.  

How to prevent overflow

Maintaining an overflow drain is fairly straightforward, and proper maintenance will prevent many problems down the road. 

  • Be mindful of the material that flows through your pipes, please refrain from pouring heavy chemicals, oils or viscous material down the drain.
  • Whenever possible, use a snake to fish out hair clumps and obstructions to prevent your pipes from becoming clogged or obstructed.

An overflow drain is a valuable asset to have in any bathroom. It is a great safety net for those with a hectic and busy schedule yet still want to enjoy their bathtub. Remember that while it is a great addition to your bathtub, it is also a separate set of pipes that need to be maintained and properly cared for unless you want further headaches down the road. 

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