How To Add an Overflow to a Bathtub

Bathtub overflows are safety features that prevent water from spilling over the edge and flooding your home. When the water level in the tub reaches a certain height, it flows into the overflow opening and down the drain. Not every tub has an overflow, but international building codes now require them. If your tub lacks an overflow, it might be wise to update it to keep your bathroom safe and compliant.

This Old House plumbing and heating expert Richard Trethewey demonstrates how to remove an old spout and install a modern overflow system.

Types of Overflow Systems

There are a few types of overflow systems on the market, each with its own distinct set of features. They’re sold in kits with the proper fasteners.

Some common overflow models include:

• Traditional overflow plates: These plates are the most common type and typically come with a separate drain stopper.
• Toe-touch systems: Toe-touch systems combine the overflow and drain into a single, cohesive unit. They can be activated by simply pressing the drain.
• Pop-up overflow drains: Pop-up overflows work by lifting and lowering a stopper within the drain. They’re sleek systems that can add a modern touch to your tub.
• Cable-driven overflow/drains: These systems use a cable mechanism to control the drain stopper. They can offer more flexibility in placement and are often easier to install than traditional setups.

Preparing for an Overflow Installation

Prepare for the installation by determining the type of overflow you need and where any new openings need to be.

Tools and Materials Needed

Besides the overflow kit, you’ll need these tools and materials: 

• Adjustable pliers
• Basin wrench
• Open-ended wrench
• PVC primer and cement
• Plumber’s putty
• Reciprocating saw
• Safety equipment (work gloves and respirators)
• Screwdriver

Assessing Your Current Setup

Take a close look at your existing bathtub setup. If you have an old tub without an overflow, determine the best spot for the new opening. If necessary, look behind the tub to make sure there’s enough space for the overflow pipe. Obstructions in the way will make the process a bit more difficult, so have a few alternate spots in mind.

Bathtub Overflow Installation Process

Follow these steps to install your overflow:

Removing Old Components

In the video, Trethewey works on an early apron-style bathtub with an access panel in the next room. He starts by turning off the tub’s water supply, then unscrews and removes the old spout. The space is a bit tight with the old plumbing layout, but the job’s made easy with a few special wrenches that can reach behind.

Finally, Trethewey disconnects the old drain shoe with a reciprocating saw before unscrewing it by hand.

Installing the New Drain

Now that the way’s been made for the new drain and overflow, Trethewey starts by installing the new drain shoe, tailpiece, and toe-touch drain. This sets the stage for the rest of the installation, and you’ll need a helper from here so everything goes smoothly.

First, apply plumber’s putty to the new drain. If possible, insert it into the empty drain hole from the access panel side. Have your helper hold the shoe on the outside while you tighten the drain from inside the tub with an open-ended wrench. Wipe off any oozing putty with a rag.

Adding the Overflow

Once the drain’s installed, it’s time to add the overflow. Have your helper place the back of the overflow and its gasket through the upper hole in the tub from the access panel side.

From inside the tub, secure the overflow by tightening the nut from the overflow kit. Attach the decorative cover plate to the overflow on the bathtub side.

Connecting the Plumbing

Once the overflow and drain are in place, you’ll need to assemble the plumbing connections correctly:

1. Measure and cut PVC pipes to connect the overflow to the existing drain line.
2. Dry-fit all components for proper alignment.
3. Once satisfied with the fit, apply PVC primer and cement to make permanent connections.
4. Install a new P-trap if necessary to accommodate the new overflow system.

Bath Overflow Testing and Troubleshooting

Once the cement has set, you’re ready to turn the water supply back on and test the new overflow system. Close the stopper and keep the water filling until it reaches the overflow. 

Then, shut the water off and check the stopper’s watertight seal. Adjust the linkage if necessary for a good seal or easier operation. The stopper should also open fully to allow for proper drainage.

At all stages of the testing process, make sure that there are no leaks at the joints and connections. Finding the problems early will prevent water damage later on.

Overflow System Maintenance Tips

Proper maintenance ensures the longevity and effectiveness of your new bathtub overflow system. Clean the overflow plate and drain at the same time as the rest of your tub so soap scum and hair don’t clog up the works. You can also install a drain screen to catch hair so it doesn’t enter the plumbing.

As you use your new drain, don’t flush large amounts of bath bombs or oils that can leave residue in the pipes. Hot water can help clear buildup, though it doesn’t negate the need to snake the drain occasionally.