How to Replace a Bathtub Drain Flange

Begin by thoroughly cleaning the bathtub, especially around the drain area, to remove any soap scum, grime, or residue. Once clean and dry, place an old towel or a non-slip rubber mat in the bottom of the tub. This crucial step protects the tub's delicate surface from accidental scratches or dings from your tools during the replacement process. Gather all the tools and materials you will need and place them on the towel for easy access.

For the assumed push-and-pull stopper, ensure it is in the open ('up') position. Firmly grip the round knob on top of the stopper and rotate it counter-clockwise to unscrew it. If it's tight, you can wrap a rag around it and use pliers for a better grip. Once the knob is off, you will see a brass post with a slot in its center, which is threaded into the flange's crossbars. Use a large flathead screwdriver or the tips of your pliers to engage this slot and unscrew the post by turning it counter-clockwise until it's completely removed.

This is often the most challenging part of the job. Insert your drain removal tool, such as a drain key, into the drain opening. Ensure the tool's prongs fit securely into the crossbars of the flange. To gain leverage, slide the long handle of a pair of pliers or the shaft of a large screwdriver through the hole(s) at the top of the drain removal tool, creating a T-handle. Apply firm, steady downward pressure while turning the handle counter-clockwise. You may feel a 'pop' as the old putty seal breaks. Continue turning until the old drain flange is completely unthreaded from the drain shoe below.

With the old flange removed, you'll see a ring of old, hardened plumber's putty. Use a plastic putty knife or the edge of an old credit card to carefully scrape all of this old putty off the surface of the tub around the drain opening. Avoid using metal scrapers which can easily scratch the tub finish. Once the bulk is removed, use a clean rag dampened with denatured alcohol or mineral spirits to wipe away any remaining oily residue. Use a small wire brush to gently clean the threads inside the drain shoe to ensure the new flange can be installed smoothly without cross-threading.

Take a generous amount of fresh plumber's putty and warm it in your hands. Roll it out into a uniform, snake-like rope about 1/4-inch to 3/8-inch thick. Press this rope firmly and evenly onto the underside of the new drain flange's lip. Some tub materials like acrylic can be stained by plumber's putty, in which case a bead of 100% silicone sealant is a better choice. Carefully position the new flange over the drain opening and begin turning it clockwise by hand. Ensure it is threading in straight and not cross-threading. Hand-tighten it as much as possible, then use your drain removal tool to give it a final quarter to half turn to snug it down firmly. This action will squeeze out the excess putty, creating a perfect watertight seal.

Once the flange is tightened, a ring of excess plumber's putty will have squeezed out. Use your finger or the plastic putty knife to neatly remove this excess putty. Follow up with a soft, clean rag to wipe away any remaining residue for a clean, professional finish. Now, reinstall the stopper mechanism. Screw the central brass post back into the crossbars, and then screw the stopper knob onto the post. Adjust the post's height so that when the stopper is closed, it sits flush and creates a good seal, and when open, it allows water to drain freely.

The final step is to test your work. Close the drain stopper and fill the tub with several inches of water. Let the water sit for at least 10-15 minutes. While it's sitting, if you have access from below, check the drain assembly for any signs of drips. If you don't have access, keep a close eye on the ceiling of the room directly below the bathtub for any new water stains. After waiting, open the drain and let all the water drain out, again checking for any leaks as the water flows through the pipe. If no leaks are found, the job is complete.