What you're actually replacing when you replace a drain

A bathtub drain is not one thing—it's a system of parts that work together. The visible part you see is the drain cover or strainer, which sits on top. Below that is the drain body (the fitting that screws into the tub itself), and underneath the tub is the P-trap (the curved pipe that holds water to block sewer gases). Most of the time, you only need to replace the drain body and strainer—the parts you can reach from inside the tub. The P-trap stays in place unless it's cracked or leaking from underneath.

The job itself is straightforward if you have basic tools and access under the tub. If your tub sits on a concrete slab or you have no crawlspace below, you may need to cut into the floor or call a plumber. Most homeowners can handle this in an afternoon.

Key Takeaways

  • You will need a drain body kit (the fitting that screws into the tub), a new strainer basket, and plumber's putty or silicone caulk—all available at any hardware store for under $30.
  • The old drain body unscrews from underneath the tub, so you need access to the space below (a basement, crawlspace, or the area under a platform tub).
  • If you cannot reach underneath, you can sometimes remove just the strainer from the top, but replacing the full drain body requires access from below.
  • The job takes 30 minutes to an hour once you have the parts and tools, and does not require soldering or special plumbing skills.

Tools and materials you will need

Gather these before you start. You will need an adjustable wrench or pipe wrench (to grip the drain body underneath), a screwdriver (usually flathead, to remove the strainer basket), a putty knife (to scrape old putty), and a flashlight (to see under the tub). A bucket catches water that drains from the P-trap when you disconnect it.

For materials, buy a drain body kit that matches your tub's size (standard is 1.5 inches). The kit includes the drain body, a rubber gasket, and sometimes a locknut. You will also need a new strainer basket (the basket that sits inside the drain opening), plumber's putty or silicone caulk (to seal the drain body to the tub), and plumber's tape (to wrap the threads so the connection does not leak). All of these cost under $30 total at a hardware store.

How to remove the old drain from underneath

Turn off the water supply to the tub if you have a shutoff valve. Go underneath the tub (in the basement or crawlspace) and locate the drain body—it looks like a metal fitting with threads sticking out. You will see the P-trap connected to it. Place a bucket underneath the P-trap connection, then use your wrench to loosen the slip nut (the large nut that holds the P-trap to the drain body). Turn it counterclockwise by hand once it is loose enough.

Once the P-trap is disconnected, use your wrench to grip the drain body itself (not the threads) and turn it counterclockwise. It will unscrew from inside the tub. You may need to hold a wrench on the nut underneath while you turn the body from above—have someone help if you can. Once it is loose, unscrew it by hand the rest of the way.

Go back to the top of the tub and pull out the old strainer basket and drain body. You will see old putty around the drain opening—scrape this away with your putty knife until the opening is clean and dry.

Installing the new drain body and strainer

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). This putty seals the gap between the drain body and the tub so water does not leak underneath.

Insert the new drain body into the opening from the top of the tub. Go underneath and hand-tighten the locknut onto the threads, then use your wrench to tighten it another quarter turn. Do not over-tighten—you only need it snug enough that it does not leak. Wipe away any excess putty that squeezes out around the flange.

Reconnect the P-trap to the drain body by hand-tightening the slip nut, then use your wrench to tighten it another quarter turn. Check that the bucket underneath stays dry for a few minutes. If water drips, tighten the slip nut a little more.

Back at the top of the tub, insert the new strainer basket into the drain opening. It should sit flush with the drain body. If your tub has a pop-up stopper instead of a basket, follow the instructions that came with your new drain kit—the mechanism is slightly different but the drain body installation is the same.

When you cannot access the space underneath

If your tub is built into a concrete slab or sits on a platform with no crawlspace, you have two options. The first is to replace only the strainer basket from the top. Unscrew the old basket (usually by turning it counterclockwise with your hand or a flathead screwdriver) and screw in a new one. This fixes a clogged or broken basket but does not replace the drain body itself.

The second option is to call a plumber. Replacing the full drain body without access from below requires cutting into the floor or removing the tub, which is beyond a typical homeowner job. A plumber can assess whether the drain body itself is the problem or whether the issue is the P-trap or the main line.

Testing for leaks after installation

Fill the tub with a few inches of water and let it sit for 10 minutes. Go underneath and check the drain body connection and the P-trap connection for drips. If you see water, tighten the slip nut a quarter turn and check again. If water is coming from around the flange (where the drain body meets the tub), the putty seal may not be tight—drain the tub, remove the drain body, and reapply putty more firmly.

Once the tub holds water without leaking, you can use it normally. The putty will harden over the next 24 hours and create a permanent seal.

Common mistakes that cause leaks

The most common mistake is over-tightening the locknut underneath. This can crack the rubber gasket or strip the threads, which then leaks. Tighten only until snug—you should not need a wrench to turn it more than a quarter turn after hand-tightening.

The second mistake is not cleaning away all the old putty before installing the new drain body. Old putty prevents the new flange from sitting flat against the tub, which breaks the seal. Scrape the opening completely clean and wipe it dry with a cloth.

The third mistake is forgetting to wrap plumber's tape around the threads of the drain body before screwing it in. This tape fills tiny gaps in the threads and prevents leaks at the connection underneath. It costs a dollar and takes 30 seconds.

Frequently Asked Questions

Can I replace just the strainer basket without removing the drain body?

Yes. The strainer basket unscrews from the top of the drain body. If the basket is cracked or the drain is slow because of debris stuck in the basket, you can replace just that part without touching anything underneath. It takes two minutes and costs under $5.

What if the drain body is stuck and will not unscrew?

explore a penetrating oil (like WD-40) around the threads where the drain body meets the tub and let it soak for 30 minutes. Then try again with your wrench. If it still will not budge, you may have corrosion or mineral buildup—a plumber has tools to remove it without damaging the tub.

Do I need to replace the P-trap when I replace the drain?

Only if it is cracked, leaking, or corroded. If it is plastic and in good condition, you can reuse it. If it is old galvanized steel and shows rust, replacing it at the same time prevents future leaks. A new P-trap costs $10 to $20.

What is the difference between plumber's putty and silicone caulk?

Plumber's putty is reusable and does not harden permanently, so you can remove it later if you need to replace the drain again. Silicone caulk hardens and lasts longer but is harder to remove. Either works—putty is easier for a first-timer.

How long does the putty take to set?

Plumber's putty hardens over 24 hours, but you can use the tub after a few hours once the water test shows no leaks. Silicone caulk takes 24 to 48 hours to cure fully, so wait a full day before running water if you use caulk instead of putty.