Replacing a worn or leaking bathtub drain doesn't require a professional plumber or an expensive service call. With a specialized drain key, a fresh container of plumber's putty, and about forty-five minutes of your time, you can swap out an old, corroded drain flange and seal up potential water damage before it rots your subfloor.
The primary challenge in this project isn't complex pipe fitting—it's dealing with decades-old, corroded metal threads that refuse to budge. If you approach the task with the right tools and a slow, steady hand, you'll avoid cracked tubs and broken crossbars. Let's look at how to tackle the job from start to finish.
Gather Your Tools and Materials
Before you unscrew a single part, make sure you have everything staged near the tub. Working without the correct tools turns a quick afternoon fix into a frustrating trip back to the hardware store.
- Tub drain wrench (or drain key): A specialized tool with cross-shaped ends that grips the internal bars of the drain flange.
- Adjustable wrench or pliers: Used to grip the drain key or provide extra leverage if the flange is stuck.
- Plumber's putty: Essential for creating a watertight seal beneath the new drain flange lip.
- Putty knife or plastic scraper: For cleaning away hardened old putty and debris without scratching the tub.
- New drain assembly: Match your existing stopper style (toe-touch, lift-and-turn, or push-pull) and finish.
- Penetrating oil: Such as WD-40 Specialist to loosen severely rusted metal threads.
- Clean rags and rubbing alcohol: For degreasing and wiping the mating surfaces completely dry.
Step 1: Remove the Old Stopper and Flange
You can't access the main drain threads until the stopper and old flange are completely out of the way. How you remove the stopper depends entirely on its mechanism. For another perspective on this event, check out the latest coverage from Reuters.
If you have a toe-touch or lift-and-turn stopper, open it fully. Look for a small set screw underneath the cap, or simply twist the entire stopper counter-clockwise until it unscrews from the crossbar. For a trip-lever style, unscrew the faceplate on the overflow drain and carefully pull out the internal linkage rod and rocker arm.
Once the stopper is gone, look down into the drain hole. You'll see a metal crossbar inside the drain flange. Insert your drain key so its prongs lock securely against those bars.
Slide your adjustable wrench onto the square handle of the drain key. Turn counter-clockwise with steady, firm pressure. If the drain doesn't budge, don't jerk the wrench or strike it with a hammer—you'll shatter the crossbars. Instead, spray a few drops of penetrating oil around the outer rim, wait fifteen minutes, and try again.
Step 2: Clean the Drain Shoe and Seating Area
A watertight seal depends entirely on a clean surface. Once you unscrew and lift out the old flange, you'll find a crusty layer of old plumber's putty and mineral buildup on the porcelain, fiberglass, or acrylic surface of the tub.
Use your plastic scraper or putty knife to gently chip away the old residue. Dampen a rag with rubbing alcohol to dissolve any remaining grease or sticky film.
Wipe the area until the metal drain shoe threads and the surrounding tub surface are completely smooth and dry. If you leave even a small lump of old putty behind, the new flange won't sit flush, creating a tiny channel for water to leak down through your ceiling.
Step 3: Prepare and Apply the Plumber's Putty
Take a golf-ball sized chunk of plumber's putty and roll it between your palms until it forms a long, pencil-thin rope.
Wrap this rope evenly around the underside lip of your new drain flange. Make sure the circle is continuous and overlaps slightly at the ends. Don't push putty down into the threaded shaft; putty belongs exclusively between the flat underside of the flange and the top surface of the bathtub basin. The metal threads themselves rely on a clean, metal-to-metal dry fit.
Step 4: Install the New Drain Flange
Take your new drain flange and lower it gently into the drain hole. Line up the threads with the drain shoe beneath the tub by hand.
Rotate the flange clockwise only by hand for the first few turns. If it feels gritty or binds up immediately, back it out—cross-threading can ruin the shoe underneath your tub, turning a simple fix into a major plumbing repair.
Once it catches smoothly, insert your drain key and tighten it down. As you tighten, excess plumber's putty will squeeze out from beneath the rim in a neat little ring. Stop turning once the flange feels snug and firmly seated against the tub.
Overtightening can crack porcelain or warp acrylic tubs. Wipe away the excess squeezed-out putty with a clean rag or your finger.
Step 5: Reinstall the Stopper and Run a Leak Test
Thread your new stopper into the center of the drain flange, or slide the trip-lever linkage back into the overflow pipe if your system uses one.
Before you put your tools away, you need to verify that your work is completely watertight. Close the drain stopper tightly and run three or four inches of water into the tub.
Dry the outside of the tub directly beneath the drain using a towel. Grab a flashlight and check the P-trap and drain shoe connections from below (either through an access panel or in the basement/crawlspace). Wait twenty minutes, then check again for any slow drops or damp spots. If everything remains bone dry, your installation is complete.
Common Mistakes to Avoid
DIY plumbing projects often go sideways because of a few small shortcuts. Keep these pitfalls in mind while you work.
- Skipping the cleanup phase: Leaving old, dried-out putty on the tub surface prevents the new flange from sealing evenly.
- Overtightening the flange: Applying excessive force with a cheater bar on your wrench can crack an acrylic or fiberglass tub basin.
- Using thread sealant instead of putty: Putting paste or thread tape on the flange lip creates a weak seal. Putty provides the necessary thickness to bridge tiny surface imperfections.
- Dropping parts down an open pipe: Always stuff a rag into the open drain shoe while cleaning so screws or tools don't slip out of reach.
Frequently Asked Questions
Can I use silicone instead of plumber's putty?
Silicone creates a strong waterproof bond, but it acts almost like an adhesive. If you ever need to remove the drain flange again in the future, silicone can lock the metal threads in place, making the flange nearly impossible to unscrew without damaging the tub. Plumber's putty stays pliable and lets you service the drain easily years down the road.
What should I do if the crossbars inside the old drain break off?
If the crossbars snap under pressure, your drain key will no longer work. You can buy an internal expansion wrench—often called an internal pipe wrench or internal drain removal tool—that grips the inside walls of the drain cylinder by expanding outward as you turn it.
Why is my new bathtub drain still leaking after replacement?
A leak right after installation usually means the rubber gasket underneath the tub shifted out of place, or not enough plumber's putty was used under the flange lip. Drain the tub, unscrew the flange, clean off the old sealant, and reinstall with a slightly thicker rope of putty.
Do I need to turn off my home's main water supply for this project?
No, replacing a bathtub drain does not require turning off the main water supply. You are only working on the waste and overflow components, which are not under pressure. Just make sure nobody turns on the faucet while you have the drain disassembled.
