What You're Actually Replacing

A bathtub drain has three main parts: the drain body (the fitting that sits in the tub floor), the drain pipe (what carries water away underneath), and the stopper mechanism (what stops the water). Most drain problems come from the stopper or a clog in the pipe itself. A full replacement means removing the old drain body and installing a new one—a job that takes two to four hours if you've never done it, and requires access to the space below the tub.

Before you commit to replacement, check whether you actually need it. If water drains slowly, try a plunger or a drain snake first. If the stopper won't hold water, you may only need to replace the stopper mechanism, not the entire drain. If water leaks from under the tub when you fill it, the drain body itself is failing and replacement is the right fix.

Key Takeaways

  • You need access to the underside of the tub—either from a basement below or by removing the wall behind it—before you can replace the drain body.
  • The drain body is held in place by a large nut underneath; you remove this nut, pull out the old drain, and screw in a new one from above.
  • Drain bodies come in different sizes (typically 1.5 inches) and styles (pop-up, plunger, or straightforward overflow); measure your old one or bring it to the store.
  • You will need a pipe wrench, plumber's putty or silicone caulk, and possibly a hacksaw if the old drain is stuck.
  • The entire job is doable without a plumber, but if you cannot access the underside of the tub, you will need to cut into drywall or remove the tub itself.

Check Your Access Before You Start

The single biggest obstacle to replacing a drain is reaching the nut that holds it in place. This nut sits directly under the drain body, on the underside of the tub floor. If your tub is on the second floor or the basement is finished, you may not have a clear path to it.

Walk to the space below your tub. If it's an unfinished basement or crawl space, you can see the drain assembly from underneath—you're good to go. If the space is finished or there is no basement, look at the wall behind the tub. If it's a shared wall (between your bathroom and another room), you may be able to access it from that side. If the wall is exterior or you have no access, you will need to either cut into drywall or remove the tub, which is a much larger job. In that case, call a plumber.

Remove the Old Drain Body

Turn off the water to the tub and open the faucet to release pressure. From underneath the tub, locate the large nut holding the drain body in place. Use a pipe wrench to grip this nut and turn it counterclockwise. The nut will be tight—explore steady pressure rather than jerking. If it won't budge after a minute of effort, spray it with penetrating oil (like WD-40) and wait 15 minutes before trying again.

Once the nut is loose, unscrew it by hand and set it aside. You may see water or debris fall—have a bucket ready. From above the tub, grip the drain body itself and pull it straight up and out. If it's stuck, you can tap gently around the rim with a rubber mallet, or use a hacksaw to cut a slot in the drain body so you can pry it out. Do not force it so hard that you crack the tub.

Clean the drain hole thoroughly. Use a putty knife to scrape away old plumber's putty or caulk, and wipe the area dry with a cloth. Any old material left behind will prevent a watertight seal on the new drain.

Install the New Drain Body

Before you install, confirm that your new drain body matches the old one. Check the diameter (usually 1.5 inches for standard tubs) and the type of stopper mechanism. Bring the old drain to the store if you're unsure.

Roll a rope of plumber's putty about the thickness of a pencil and press it around the underside of the new drain body's flange (the flat part that sits on top of the tub). Alternatively, use a bead of silicone caulk, which is more water-resistant but takes longer to cure. Do not use both.

From above, insert the new drain body into the hole and press it down firmly so the putty or caulk spreads evenly around the rim. From underneath, thread the large nut onto the drain body by hand first, then use the pipe wrench to tighten it. Turn clockwise until snug—do not over-tighten, as this can crack the tub or strip the threads. The nut should be tight enough that you cannot turn it by hand, but you should not need to strain with the wrench.

If you used plumber's putty, let it cure for 24 hours before running water. If you used silicone caulk, check the manufacturer's instructions; most require 24 to 48 hours.

Reconnect the Drain Pipe and Test

Once the drain body is installed and the sealant has cured, reconnect the drain pipe underneath. The pipe should slip onto the outlet of the drain body. If it's a slip-fit connection, tighten the hose clamp with a screwdriver. If it's a threaded connection, hand-tighten first, then use a wrench to snug it another quarter-turn.

Turn the water back on and fill the tub halfway. Watch from underneath for any drips around the drain body or at the pipe connection. Small beads of water on the outside of the nut are normal during the first fill, but a steady drip means the seal is not tight. If that happens, turn off the water, let it dry, and tighten the nut another quarter-turn.

Drain the tub and observe the water flow. It should drain smoothly without gurgling or backing up. If it drains slowly, you may have a clog further down the line, not a problem with the new drain body.

Common Mistakes to Avoid

The most common error is over-tightening the nut, which can crack the tub or strip the threads on the drain body. Tighten until snug, then stop. If you hear cracking sounds, back off when ready.

Another mistake is installing the drain body before the sealant is ready. If you use plumber's putty, it needs to cure for a full day. If you run water too soon, it will seep under the flange and cause leaks. Silicone caulk takes even longer, so read the label.

A third error is forgetting to clean the old sealant from the tub before installing the new drain. Any old putty or caulk left behind will prevent a watertight seal. Spend five minutes scraping and cleaning—it's worth it.

Finally, do not assume the new drain body will fit the old hole perfectly. Drain holes can vary slightly in size or shape. If the new drain body does not sit flush against the tub, you may need to enlarge the hole slightly with a file or drill. Test-fit before you explore sealant.

When to Call a Plumber Instead

If you cannot access the space underneath the tub, stop and call a plumber. Cutting into drywall or removing the tub is beyond a typical first-time job and can damage your home if done wrong.

If the old drain body is corroded or broken and you cannot remove the nut, a plumber has specialized tools to extract it without damaging the tub. If you crack the tub during removal, the tub itself will need repair or replacement, which is expensive.

If you are uncomfortable working with plumbing connections or you have already tried and encountered leaks you cannot stop, a plumber will finish the job correctly and stand behind the work with a warranty.

Frequently Asked Questions

Can I replace just the stopper instead of the whole drain?

Yes. If water drains fine but the stopper won't hold water, you only need to replace the stopper mechanism. Most stoppers unscrew from the drain body or pull straight out. Bring the old stopper to the store to match the type and size. This takes 10 minutes and costs $15 to $40.

What if the drain body is stuck and won't come out?

Spray the nut with penetrating oil and wait 15 to 30 minutes. Try again with the wrench, explore steady pressure. If it still won't budge, use a hacksaw to cut a vertical slot in the drain body, then use a flat-head screwdriver in the slot to pry it out gently. Do not hammer or force it, as you risk cracking the tub.

Do I need plumber's putty or can I use caulk?

Either works, but they have different properties. Plumber's putty is easier to remove later if you need to replace the drain again. Silicone caulk is more water-resistant and lasts longer, but it's harder to scrape away. For a first-time job, plumber's putty is more forgiving. Use one or the other, not both.

How long does the sealant need to cure before I can use the tub?

Plumber's putty needs 24 hours. Silicone caulk typically needs 24 to 48 hours, depending on the brand and humidity. Check the label on your product. Running water before the sealant is fully cured will cause leaks underneath the tub.

What size drain body do I need?

Most standard bathtubs use a 1.5-inch drain body. Measure the diameter of your old drain or bring it to the store to confirm. Some older or specialty tubs may use 1.25 inches or 2 inches. The drain body must match the hole size in your tub, so get this right before you buy.