How to Install Drain in Bathroom Sink: Step-by-Step
Learn how to install a bathroom sink drain with a complete, beginner-friendly guide. From choosing the right kit to leak-testing, follow Drain Guide's step-by-step approach for a secure, drip-free drain.
In this guide, you will learn how to install a bathroom sink drain from start to finish. You'll identify the right kit, replace the old hardware, assemble the new drain, seal joints, and perform a leak test. Gather basic tools, a bucket, and towels before you begin. Expect a few tighter spaces under the sink and a loose pipe at first check.
Assess Your Sink and Drain Type
Before you buy a new drain, inspect the sink layout and measure the drain hole diameter. Most bathrooms use 1.25-inch or 1.5-inch drain outlets; match the flange size to avoid leaks. If the current assembly includes a pop-up stopper, decide whether you want a similar style or a modern, button-operated version. Consider material compatibility: metal drains with metal tails require different gaskets than plastic ones. Check the P-trap alignment and the wall pipe for signs of corrosion. Having a plan avoids returning parts mid-project. Take photos of the existing setup from multiple angles so you can compare with the new kit. Verify you have a clean under-sink area; remove cabinet items to gain space. If your sink uses a non-standard size or an unusual tailpiece, you may need an adapter. For porcelain sinks, a fiber gasket and plumber's putty are common; for metal sinks, silicone sealant may be preferred if the kit lacks a washer. Finally, decide if you want to replace the P-trap or reuse the existing, provided it is in good condition and matches the new drain assembly.
Gather Tools, Materials, and Prep the Work Area
Plan your workstation before dismantling anything. A well-lit space with a dry, clean surface reduces mistakes. Gather a drain assembly kit compatible with your sink hole, plus essential hand tools such as a basin wrench, adjustable wrench, and slip-joint pliers. Have a bucket, towels, and a flashlight handy to manage water and visibility under the sink. Use plumber’s putty or silicone sealant as recommended by the drain kit instructions. Sort washers and gaskets by size and type and lay them out in order of assembly. If you’re replacing a pop-up stopper, confirm the linkage and stopper type match the new kit. Finally, read the kit’s instructions to understand the order of parts and any required sealants or compounds.
Remove the Old Drain and Clean the Basin
Shut off the water supply and drain any standing water from the sink. Loosen the slip nuts on the P-trap and tailpiece, then carefully lift out the old drain assembly. Use a putty knife to scrape away old putty or sealant from the sink bottom and flange. Inspect the sink hole for chips or cracks; if you see damage, stop and repair or replace the sink mounting hardware before proceeding. Clean all threads and surfaces with a rag, ensuring a dry, dust-free area. Take this opportunity to verify the hole diameter and the presence of a suitable gasket or washer for the new drain. If the old kit used lead-based or degraded materials, exercise extra caution and replace those components with modern alternatives.
Install the New Drain: Fitment, Seals, and Alignment
Apply a liberal bead of plumber’s putty or a gasket as directed by the kit to the flange bottom. Insert the new drain through the sink hole and begin tightening from beneath with the appropriate wrench. Install the tailpiece and slip-joint nut, then loosely connect the P-trap. Tighten the nuts evenly by hand first, then snug with a wrench, taking care not to overtighten and crack plastic components. Recheck alignment of the drain with the trap and wall pipe; minor adjustments can prevent leaks. If your kit includes a pop-up mechanism, reconnect the linkage, test the stopper, and ensure smooth operation. Finally, wipe away any excess sealant and confirm a clean, flat seal against the sink bottom.
Reconnect P-trap, Test for Leaks, and Final Checks
With everything mounted, reattach the P-trap to the drain arm and ensure all connections are tight but not over-torqued. Run water into the sink slowly to check for leaks around the flange, slip joints, and trap nuts. If you detect a leak, tighten the corresponding nut in small increments and re-run the test. If leaks persist, reseal with an appropriate sealant or replace an o-ring. Once the test passes, wipe the area dry and reinstall any cabinet components you removed. Consider applying a small amount of silicone sealant around the base of the drain flange for additional moisture resistance in humid bathroom environments. Finally, keep the area dry for a few hours and recheck after heavy use to ensure continued integrity.
Authority Sources
For safety and best practices, consult these sources: https://www.osha.gov, https://www.cdc.gov, https://nkba.org
Tools & Materials
- Drain assembly kit (flange, tailpiece, nuts, washers)(Choose kit compatible with 1.25)
Steps
Estimated time: 60-120 minutes
- 1
Shut off water supply
Locate the under-sink shutoff valves and turn them clockwise until closed. This prevents water from spilling while you work and protects both you and the fixtures. Never work on live valves or force a valve that won’t turn.
Tip: If valves are stiff, apply gentle penetrating oil and wait a few minutes before attempting again. - 2
Prepare the workspace
Clear the area and place a bucket and towels under the trap area. This catches debris and water, keeping your cabinet dry. Take a photo of the existing setup for reference, which helps you replicate the correct alignment later.
Tip: Use a flashlight to inspect hard-to-see corners and identify any corrosion or wear. - 3
Remove the old drain
Loosen the slip nuts on the P-trap and tailpiece with a wrench. Slide the nuts off and carefully lift the old drain assembly out from the top. Clean the surface and remove old sealant or putty from the sink underside.
Tip: Keep the nuts in order so you can reuse them if compatible with the new kit. - 4
Clean and inspect the sink hole
Wipe the hole edge clean. Look for cracks or chips around the flange area. If damage is present, plan to repair or replace components before continuing.
Tip: A clean, flat surface ensures a proper seal and helps prevent future leaks. - 5
Install the new drain flange and seal
Apply plumber’s putty or a gasket on the flange bottom as directed by the kit. Insert the flange through the sink hole until it sits flush. From beneath, thread the lock nut and tighten.
Tip: Go finger-tight first, then snug with a wrench. Avoid overtightening plastic parts. - 6
Attach tailpiece and align the drain
Connect the tailpiece to the drain body and secure with the slip nut. Ensure the tailpiece is vertical and aligned with the P-trap to prevent misrouting of water. Keep connections snug to avoid leaks but leave room for adjustments.
Tip: If a pop-up stopper is used, ensure linkage is properly attached for smooth operation. - 7
Reconnect P-trap and supply lines
Reattach the P-trap to the drain arm and ensure all slip joints are snug. Reconnect any supply lines to the faucet. Check that the hardware doesn’t cross-thread and that the joints are clean.
Tip: Always tighten in small increments and test before finalizing the cabinet setup. - 8
Test for leaks and finalize
Turn the water back on at the shutoff valves and run water into the sink. Check all joints for leaking around the flange, tailpiece, and P-trap. If you see leaks, re-tighten joints a bit more or re-apply sealant as needed.
Tip: Keep a dry towel handy during testing to quickly catch any drips.
Got Questions?
Do I need to remove the sink to install a drain?
Usually you don’t remove the entire sink; you work from beneath the cabinet. In rare cases, a more involved install may require moving cabinets or temporarily removing the sink hardware. Most DIYers complete this under the sink with basic tools.
You usually don’t have to remove the sink; work from underneath the cabinet and you’ll be able to access the drain.
What drain kit should I buy for a porcelain sink?
Choose a kit that includes a metal or plastic flange compatible with porcelain finishes. Check for a plain rubber gasket or a compression seal, and ensure the tailpiece length suits your setup. If in doubt, a standard 1.25- or 1.5-inch drain kit will fit most porcelain sinks.
Select a standard 1.25- or 1.5-inch drain kit made for porcelain sinks, with a gasket or seal that fits your flange.
Can I use silicone sealant instead of plumber’s putty?
Both are used to seal drains; putty is common for metal drains, while silicone sealant works well for porcelain or non-metal surfaces. Always follow the kit’s instructions. Silicone typically provides a longer-lasting seal in damp bathroom environments.
Yes, silicone sealant can be used in many setups, but follow your kit’s guidance for best results.
How do I know if a leak is from the tailpiece or P-trap?
Tighten connections one by one and re-test. If a leak persists after tightening the tailpiece, inspect the P-trap joints last. A leak at the sink flange usually indicates an improper seal at installation.
Test each joint individually to pinpoint leaks and re-seal as needed.
Is it dangerous to work under the sink?
Working under a sink is generally safe if you shut off water, keep the workspace dry, and use proper tools. Avoid forcing parts and be mindful of sharp edges. If you feel unsure, pause and seek professional help.
It’s usually safe if you shut off water and stay careful; if unsure, consider hiring a pro.
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The Essentials
- Prepare your space and tools before starting
- Choose a drain kit compatible with your sink hole size
- Seal joints properly and test for leaks after install
- Document steps with photos to guide reassembly
