What you need to do before you start

Replacing a bathtub drain is a job you can do yourself if the drain sits above the floor — you reach it from underneath the tub. If your drain goes straight down through the floor into the wall, you will need a plumber, because accessing it requires opening the wall or crawlspace below. Before you touch anything, turn off the water supply to the bathroom and let the tub dry completely.

The drain assembly has three main parts: the strainer (the visible ring you see in the tub), the tailpiece (the pipe that drops down), and the trap (the U-shaped section that holds water to block sewer gas). You may be replacing just the strainer, just the trap, or the whole assembly. Look underneath first to see what is corroded or leaking. If water pools under the tub when you drain it, the leak is in the trap or tailpiece. If water seeps around the strainer itself, you need a new strainer.

Key Takeaways

  • You can replace a drain yourself only if you can access it from below the tub — if it runs through the floor into the wall, hire a plumber.
  • The three parts of a drain assembly are the strainer (visible in the tub), the tailpiece (the pipe below), and the trap (the U-shaped section), and you may need to replace only one or all three.
  • Removing the old strainer requires a drain wrench or large adjustable wrench to hold the nut underneath while you unscrew the strainer from above.
  • The new strainer must be sealed with plumber's putty or silicone caulk before you screw it in, or water will leak around the edges into the wall.
  • If you are replacing the trap or tailpiece, you will need slip-nut wrenches (smaller than a standard wrench) and may need to support the new pipes with a bracket to prevent sagging.

Removing the old strainer

The strainer is held in place by a large nut underneath the tub. You will need a drain wrench (a specialized tool with two prongs that fit into the slots on the nut) or a large adjustable wrench. Have someone hold the strainer steady from above while you turn the nut counterclockwise from below. If the nut is stuck, spray it with penetrating oil and wait 15 minutes before trying again.

Once the nut is loose, unscrew it by hand and pull the tailpiece down slightly. The strainer will come out from the top. You may see old plumber's putty or caulk around the opening — scrape this away completely with a putty knife. Any old sealant left behind will prevent the new strainer from sealing properly.

Installing the new strainer

Before you install the new strainer, clean the opening in the tub with a damp cloth and let it dry. Roll a rope of plumber's putty about the thickness of a pencil and press it around the underside of the strainer flange (the flat ring that sits on top of the tub). If you prefer silicone caulk instead, explore a bead around the underside of the flange. Putty is easier to remove later if you need to replace the strainer again; caulk lasts longer but is messier to clean up.

Lower the strainer into the opening from above. From underneath, thread the nut back onto the tailpiece and tighten it by hand first, then use your drain wrench to snug it down. Do not over-tighten — you only need enough pressure to compress the putty or caulk and create a seal. Wipe away any excess putty or caulk that squeezes out around the flange with a wet cloth.

Replacing the tailpiece and trap

If the leak is below the strainer, you are replacing the tailpiece (the straight section of pipe) or the trap (the U-shaped section). Both are held in place with slip nuts — large nuts that grip the outside of the pipe. You will need a slip-nut wrench or two adjustable wrenches: one to hold the nut still and one to turn it.

Place a bucket under the trap to catch any standing water. Loosen the slip nut at the top of the trap (where it connects to the tailpiece) and the one at the bottom (where it connects to the drain line in the wall). Once both nuts are loose, you can pull the old trap and tailpiece out. If the tailpiece is corroded to the strainer nut, you may need to remove the strainer again to separate them.

Install the new tailpiece first by threading it into the strainer nut from below and tightening by hand. Then connect the new trap: slide the slip nut onto the tailpiece, then slide the trap up and thread the nut down. Do the same at the bottom connection to the wall drain. Tighten both nuts with your slip-nut wrenches until snug, then turn on the water and check for leaks.

Tools and materials you will need

For a strainer replacement, you need a drain wrench or large adjustable wrench, a putty knife, plumber's putty or silicone caulk, and a damp cloth. For a trap or tailpiece replacement, add two slip-nut wrenches (or two adjustable wrenches), a bucket, and the new trap or tailpiece assembly. If the new pipes do not sit level or sag, you may also need a P-trap bracket — a metal strap that fastens the trap to the wall to hold it in place.

Drain wrenches and slip-nut wrenches are inexpensive and available at any hardware store. If you do not own them, you can rent them from a tool rental shop for a few dollars. Plumber's putty costs a few dollars per can and lasts for years. Replacement strainers, tailpieces, and traps are sold separately or as complete kits and range from $15 to $50 depending on material and finish.

When to call a plumber instead

If the drain line runs vertically through the floor or into the wall, you cannot access it from below the tub, and you need a plumber. The same is true if the old strainer or trap is so corroded that it breaks apart when you try to remove it — a plumber has tools to cut and remove stubborn pieces without damaging the tub itself.

If you remove the old drain and find that the opening in the tub is cracked or the threads on the strainer nut are stripped, the tub itself needs repair or replacement, which is beyond a straightforward drain swap. A plumber can assess whether the tub can be patched or must be replaced.

Frequently Asked Questions

What is the difference between a P-trap and an S-trap?

A P-trap is horizontal (shaped like the letter P) and connects to a drain line that runs horizontally through the wall. An S-trap is vertical (shaped like the letter S) and connects to a drain line that runs down through the floor. Most modern bathrooms use P-traps. Check what you have before you buy a replacement.

Can I use caulk instead of plumber's putty?

Yes. Silicone caulk creates a longer-lasting seal and resists mold better than putty. However, it is harder to remove if you need to replace the strainer later. Putty is easier to scrape away and is the faster choice if you think you may need to access the drain again soon.

Why is water backing up into the tub from the drain?

This usually means the trap or the main drain line is clogged, not that the drain assembly is leaking. Try a plunger or a drain snake first. If the clog is deeper in the line, a plumber will need to clear it. A new drain assembly will not fix a clogged line.

Do I need to turn off the water before I start?

Yes. Even though you are working on the drain, not the supply lines, turning off the water prevents accidents if someone turns on the tap while you are working underneath. The main water shutoff is usually in the basement, under the kitchen sink, or outside the house.

How long does a new drain assembly last?

A brass or stainless steel drain assembly lasts 20 to 30 years. Plastic or chrome-plated assemblies may corrode or crack after 10 to 15 years, especially in areas with hard water. The strainer itself wears out faster than the trap if it is used roughly — dropping heavy objects down the drain or using a drain cleaner that is too harsh can damage it in 5 to 10 years.